I would suggest hosting your pics at Flickr, Snapfish, Adobe Photoshop Express or something similar. Make sure the pics you want to use are set to public (not private or friends only, etc.). Once you have your pics set up there, those are the links you stick between the [IMG] tags in your posts here.
For your avatar pic, go to user CP, then edit avatar (look at the column of things along left side of window). Read the stuff at the bottom about both the physical size of the pic as well as the file size. You will need to crop, save at lower resolution, etc. (wash, rinse, repeat maybe) the pic you would like to use until the site software accepts it.