When you uploaded the WP files you used FTP, right?
You can use that FTP utility to look at your files on your site. Go to where WP is installed on your site, and navigate in the WP install folders to /wp-content/themes/ and right there is where all the theme folders are. The theme you pick to use is in there, the default and the classic themes come with WP. You can upload other themes to that space too. So if you did, as it sounds like you have ...
In order to edit the files online in WP Admin, you have the "CHMOD" the theme folders to "666" to make them "writable".
So if you load a theme in WP ADMIN Theme Editor, and it gives you that message ... then you need to CHMOD to 666.
Whatever FTP you have it's doable, easier or not. Go to that theme folder you want to edit and right click and choose "Properties" is one possible way you access permissions for files. There is usually some kind of help in an FTP utility to get you to understand how to "set file permissions" which is the same thing as "CHMOD" and "CHMOD" is how one is told to set file permission to a certain level as in CHMOD "777" or CHMOD "666" either setting will allow you to edit those files in WP Admin Theme Editor. "666" is a lower permission level and that's all you need to make them writable, and the setting that is advisable.
You can also dowload those files and edit them on your computer, then re-upload them to the correct place.
In your theme folder you will find the names of files, "sidebar.php" if it's there will be where you might be entering your "about" info, somewhere near the top of the file.
WP is a PHP application. It's a valuable program, much nicer than anything Blogger has. It's not the same as Blogger therefore. You can work with it as it is, without changing anything, but it's some thing that makes for a fun learning time if you jump in and try to understand it and make a go of it.
There is the codex here:
which you can read up on how to do things there, and come back here and ask Q's as much as you need to! We love to help newcomers to WP!
In order to "customize" WP you do need to look at the individual files in your chosen theme.
Index.php is the Main page, the front page.
Your posts will show up there first.
Every post has a permalink page. You can have that page look the same as the index.php front page, or change it's look by using "single.php" which the system will recognize if it's in your theme, and your permalink single archive posts will show up on that when that permalink is clicked.
There is an Archive Template then which is the page that monthly and category, for instance, archives will show up on when called up.
That page shows multiples posts, only the "single.php" template shows just one post, with default settings.
It's easy to use WP just as it is, so it's not fair to say "it's not easy to use". It's easy right out of the box. Customization beyond that is an aquired skill just like anything is, to one degree or another. It's only a need to familiarize yourself with how to edit a file's permissions, and how to edit different theme templates in WP.
If you stick with it, give it time, do it slowly, before you know it you CAN have your WP site looking as you want it, like you had it at blogspot.
You can take that and turn it into a theme, you just need to know how.
So either figuring it out on your own is a good idea, or taking up the offer of someone here to do the conversion of your theme over might be a good idea too. :)