How to post an Avatar

As a newbie..i wanna ask how to post the little picture on the side of my post ?

Have a look around those menus at the top of the screen. Explore, do something for yourself without wanting everything on a plate for you.

even i used a jpg and gif to post..still it says please use gif or jpg
y this happens ?

and the problem also exist on deviantart when i try to post somethingon it

On deviantart, once you've uploaded your avatar open up your browser and paste this into your address bar:

http://a.deviantart.com/avatars/FIRST_LETTER_OF_YOUR_USERNAME/SECOND_LETTER_OF_YOUR_USERNAME/YOURUSERNAME.gif

Then refresh the page once it's opened. Your avatar should appear.

For here, i'm not sure.

and please use the edit button 😉