There are basically two ways of uploading pictures to this site.
The first method is to click 'post reply' then select the 'upload attachment' tab at the bottom of the reply screen, find the attachment on your hard drive, and finally click 'add the file' and you should be fine.
The second method, which I prefer, is to open a picture account with photobucket (or similar, there are several to chose from), upload the picture there according to their instructions, then copy the photo URL. Photobucket has a nice feature for doing that; otherwise just right-click on the image and select 'copy image address'. Then write [img] in your AHF post, press ctrl+v, and write [/img]
This is not half as fiddly as it sounds - learning by doing is the way to go, also in this case, and there is a test section here on the AHF where you can try it all out.