Avatars and signature pictures are just pictures found on the internet, uploaded from a camera, made in Photoshop, etc. You can google just about any image, but you have to make sure it fits the size requirements. There are some avatar websites too, but I forgot them.
Once you have a picture you want to use for your avatar, for example, here's the procedure.
Click on your name. Scroll down and click Update my Information. Scroll to the Avatar section. Copy the URL of the avatar - a URL looks like this example one - (
http://www.youravatarpicture.com) and a bunch of weird numbers and stuff. Paste the URL into the first bar, which sais "Use remote avatar". Usually it will work. Save your settings by clicking the button on the bottom of the page.
For your signature picture, find a picture you want (can be bigger than the avatar picture but try not to make it massive) and in the Signature/Timezone section, copy the URL of the picture into the space provided. At the end and front of the line, change the capital "IMG"s to lower case "img"s. That should work, and that's hwo you get your pictures up.
Making pictures is a whole different story. You have to have Photoshop, or some other editing program. It costs nearly $500, unless you download it for free off a torrent site without your parents knowing.