The forums use a Trust Level (TL) system, which grants more abilities as you participate. All new users start at Trust Level 0 (New Member). This means you won’t be able to open a new topic until Trust Level 1 (Member) to prevent spam/bots. You may wish to check this topic:
For more information on Trust Levels, requirements, and abilities, you may wish to check the following topic:
I have manually raised your Trust Level. You should be able to post new topics to any category now, which isn’t restricted or top level. You should see a button saying “New Topic” at the top.