Start New Thread is always to the upper left of the Main Topic List, not in an open topic post. so, for example, go to Forum Index on your home page, select a topic that is interesting or applicable to you, and above that first set of Titles you will see "Start New Thread".

If a member replies in a non-supportive (offensive) manner you can report them to admin by using the little red ! at the bottom left of every post. you can also put members on your IGNORE list (under Customize Profile, from the long menu on the left). this prevents them from posting on any more threads you start.

there are many more tips at the top of the Community Forum, under the Sticky: Tutorials. i hope you learn your way around soon. if you have questions, you can ask the Community Liaisons or send me a Private Message.
best wishes~
Gus