Post... well you know how to post. As for threads, new thread button which are at the top/bottom of sections. Look at the faq for stuff like this, should be mentioned there: http://www.pokecommunity.com/faq.php
...the button for previewing is on the same page for changing your signature. (UserCP, Edit Signature, and then preview signature which is next to the change signature button, although for me it previews by default anyway).
Merely an infraction, not a ban. But kindly tell me where it says in the rules you are allowed to spam like that - multiple times to boot. Only doing my job as a mod, so if you spam like that (and you got an infraction for it before), well it's only really your fault for breaking the rules you agreed to obey when joining the forums, is all. No hard feelings - just please don't go about spamming and you won't get infractions, simple as that.