Need help with BB Code

[Judaeus Apella]

Trying to figure out how to make a thumbnail you can click on for a larger version of that picture. I've seen people do it in other forums that use BB code, but I can't figure out how to do it in this forum. The code I know [thumb1=http://www.blahblah.com/picture.jpg]http://www.blahblah.com/picture.jpg[/thumb1] doesn't work, and I don't think HTML works here... so I don't know how to make this work. Anyone know how to do this?

Edit:

All I can figure out how to do is link one image to another, but I can't figure out the code to resize an image for thumbnails.