I'm going to guess you want to create a new thread in an existing forum...
Go to the front page of the particular forum you're interested in (for example, 80-86 is here:
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks - Ford Truck Enthusiasts Forums ) then click the New Thread button kind of in the top-left corner, it looks like this: