Incidentally... one of the rules is that the image must be yours. If you want to refer to an image created by another photographer (anything where you don't own the copyright) then you can insert a link to the page where the image is hosted, but the image shouldn't be embedded in the post here.
It sounds like you're really just looking to post your own work -- so this probably isn't an issue for you, but from time to time people do post "how do I make a shot that looks like this?" and then they add the image directly into the post.
Sparky linked to a post, but I noticed it's from 2007 and the user interfaces may not be the same (Flickr, for example, has updated their user interface so the functionality is all still there -- it just doesn't look like the instructions in the post.)
I find it easier to use another site where I host my images anyway and then just embed the BBCode to link the image into the post on this site. But sometimes if the image was shot specifically to illustrate a concept (not something I'd normally want people to think of as photographic art) then I might just upload it directly to this site and not bother to post it to Flickr and link it.