If you want to make your signature visable, aka have pictures and writting show when you post, you have to go into Profile, preferances, then towards the middle to bottom there should be one that says "Always attach my signature" select yes and then when you post it will show your sig.
To add an image that does not already have an IMG code all you have to do is click the IMG thing at the top then add the direct link/adress. You can do this by right clicking on the picture it's self, copy the adress and then past it into the IMG code creator.
If you want to use spoiler, (A black bar that when you click it the picture slides down so it takes up less space.) then you put...
[spoiler] (Place picture here) [//spoiler] Delete the second / when you type it, I only added two so the spoiler wouldn't work.