1. For the captions, first go to the User CP at the top of the page. Next click on Edit profile. Next, click in the box next to "Custom User Title" and type what you want!
2. For pictures, if you scroll down when your in the page where you type your post, you will see a button that says Manage attachments. That will let you post pictures, and other types of files.
3. For an avatar, unless you pay a subscription for it, you can't get one

. But if you do, go to the User CP, then click on Edit Avatar on the left side of the screen.
I hope this helps!