If you mean placing a picture in with your posts, there are two way.
1. Click "Reply". Then upload a picture from your computer by going to "Manage Attachments", click "Choose File", and then click "Upload". Pictures are limited to 100k in size.
2. Add a link to a picture that's stored on a photo hosting site (photobucket, flickr, picasa, etc). Copy the picture address and click the "Insert Image" icon, paste the picture address in the dialog box and click ok, then click "Submit Reply". There's no limit on the picture size.
Easy as pie wasn't it?
Pie???
This is the "Insert Image" icon.