The so-called customizer is found in Appearance -> Themes. Many users complain that the tool won’t load. This is a bug that WP so far hasn’t fixed, but (unless you have the Custom Design upgrade and you want to use the color/font tools) it’s insignificant: you don’t really need the tool. [*]
A.
The customizer simply brings together some options that are already available via the main dashboard sidebar: [*]
• You edit the blog title & tagline in Settings -> General.
http://en.support.wordpress.com/settings/general-settings/
• You set a static front page (or revert to latest posts on the homepage) in Settings -> Reading.
http://en.support.wordpress.com/pages/front-page/
• You set a header image, and hide the blog title & tagline or adjust their color (if the theme supports these options), in Appearance -> Header.
http://en.support.wordpress.com/themes/custom-header-image/
• You set a background color or a background image in Appearance -> Background.
http://en.support.wordpress.com/themes/custom-backgrounds/
• You create and activate a custom top menu in Appearance -> Menus.
https://wpbtips.wordpress.com/2011/12/19/custom-menus/
Note: the above options work in all themes, or in the majority of them. Some themes have additional options of their own (alternative color schemes or alternative layouts or other unique features). These are found in Appearance -> Theme Options. [*]
B.
The customizer only brings together some basic options. [*] There are several other options you can or should take care of, especially when starting a new blog. Among other things:
• You make your name link to your blog, and set the interface language, in Users -> Personal Settings.
http://en.support.wordpress.com/personal-settings/
• You set the blog language, set your timezone, change the time and date format, and set a blavatar (= favicon, blog pic), in Settings -> General.
http://en.support.wordpress.com/settings/general-settings/
• You edit your displayed name, add profile info, and set a gravatar (= avatar, user pic), in Users -> My Profile.
http://en.support.wordpress.com/user-profile/
http://en.support.wordpress.com/manage-my-profile/
• You set the number of posts per page (after disabling infinite scrolling), set your feed to provide summaries instead of full texts, and turn the blog to private or semi-private (or back to public), in Settings -> Reading.
http://en.support.wordpress.com/settings/reading-settings/
http://en.support.wordpress.com/infinite-scroll/
http://en.support.wordpress.com/settings/privacy-settings/
• You add or remove sidebar (or footer) widgets in Appearance -> Widgets.
http://en.support.wordpress.com/widgets/
https://wpbtips.wordpress.com/2009/09/28/the-no-widgets-paradox/
• You add share and like buttons, and select where they should or shouldn’t show up, in Settings -> Sharing.
http://en.support.wordpress.com/sharing/
• You select comment-related options in Settings -> Discussion.
http://en.support.wordpress.com/settings/discussion-settings/
Note well: changing the principal discussion setting (i.e. whether you allow or don’t allow comments) applies to posts and pages you create after you make this change. To change it on already published posts/pages, you need to edit those posts/pages; details here:
https://wpbtips.wordpress.com/2010/04/23/comments-off-1/
• You set the default widths for the thumbnail, medium and large image size options in Settings -> Media.
http://en.support.wordpress.com/settings/media-settings/
• You set your default post and link categories, and select the option “WordPress should correct invalidly nested XHTML automatically”, in Settings -> Writing.
http://en.support.wordpress.com/posts/categories/
http://en.support.wordpress.com/blogroll/link-categories/
https://wpbtips.wordpress.com/2012/05/19/sidebar-at-the-bottom-and-related-issues/
• If you have the Custom Design upgrade, you make CSS changes in Appearance -> Custom Design.
https://wpbtips.wordpress.com/2013/02/21/where-is-the-theme-css-and-how-do-i-edit-it/
_______________________
[*] Very rare exception: on a few themes the Theme Options are hidden in Appearance > Themes > Customize.
wordpress tips 
Very comprehensive guide, Panos.
Posted by Val | March 28, 2013, 21:22Thanks Panos. This will prove quite valuable down the road.
Posted by IzaakMak | March 28, 2013, 21:58Thanks! At first I thought of section A only (so I could use it as a standardized forum reply to this complaint), but while writing it I got the idea for section B, as I’ve seen that many users aren’t aware of some important options.
Posted by Panos | March 29, 2013, 20:21Hi there,
Thanks for this. Bookmarking! I played around with the customizer when it was first introduced and then abandoned using it.
Posted by timethief | March 31, 2013, 20:35“and then abandoned using it”: naturally (as the post shows)!
The only problem is the very few themes in which the Theme Options have been placed in the customizer instead of where they should be. Why WP did this is yet another mystery to me…
Posted by Panos | March 31, 2013, 20:45Part B is an excellent checklist for setting up a blog.
I’ll admit that I never paid any attention to the “customizer” because it was annoying when I simply wanted to change themes on a test blog…(ignored it in the same way my brain has learned to not see adverts in sidebars)
off-topic: just an observation
For folks who spend a lot of time online, sidebars are easy to ignore. But I realized that is not true for people who don’t spend much time on computers while I was setting up the site for my job. It’s wp.org so I can use a plugin to randomize images in sidebars. Several people said they got confused because the pic of “Sarah helping a customer” changed to “Mike carrying a bag of stuff bigger than himself” when they returned to a specific page. I put a note explaining that the pictures would change each time the page is loaded. That satisfied the board of directors, but I also wonder if people actually read?
Posted by Tess | April 1, 2013, 18:37Thanks! Yeah, it came as an afterthought but the idea was just that – to make the post more useful than a mere reply to the complaint “customizer won’t load”.
And yes, some people don’t read. I see it every other day in the forum.
Posted by Panos | April 1, 2013, 23:25oy! like today for example? I was not around so missed closing some threads that , well  ’, oy…
Posted by Tess | April 2, 2013, 07:26Mm, like yesterday rather. Today’s case suffers from a different syndrome…
Posted by Panos | April 2, 2013, 08:42OH no. I was just closing theads and answering yesterday’s. I’ll look for today’s problem tomorrow. LOL
I sufffer from too many nbsp s
… if that would be my biggest problem
Posted by Tess | April 2, 2013, 09:59CHILD PAGES, DROPDOWNS, PAGES (STATIC), THEMES
Child pages: links displayed on parent or as dropdowns
Hi Panos, sorry but I couldn’t find where to leave a reply on the above page (Child Pages). Thanks so much for your note re to hide or delete the dropdowns on the header bar. Now I have an empty black box where the 6 child (or grandchildren actually) pages were – how do I get rid of this box?
Posted by Steve Holmes | May 8, 2013, 15:52Sorry for the delayed reply: I was on vacation.
I’m not seeing any “empty black box” on the blog linked to your username, so I guess you resolved this.
As for why you can’t find where to leave a reply on older posts, see the red note in my sidebar.
Posted by Panos | May 12, 2013, 20:10nothing for font style ? :/
Posted by Reshail Yawar | May 30, 2013, 20:03Not as a free option: changing font families, font sizes etc requires the Custom Design upgrade.
Posted by Panos | June 1, 2013, 16:10