If there are new postings the SP-Studio character is reading a newspaper. So when you visit the forum you know which topics you need to read and which can be ignored because they don't have new replys.
It is the same with the gallery: A reading character means there are new images in this album you have not seen yet.
If the topic was marked as "important" by me it has an exclamation mark. Important (or "sticky") topics are always shown on top of the others, even if they don't have new replys. I do this if I want everybody to read it.
This means the topic locked. You can read locked topics, but not reply to them. A topic is locked if there should be no discussion (like the "board rules") or because it will be deleted soon. Usually there won't be many locked topics.
The old contests in the gallery are locked too.
I hope this explained it