Most, if not all, forums require you to navigate to the sub forum where you want to post your thread. Until you arrive there, you will not find a "Create Thread" button (how will the forum software know where to place your thread?).
It's very useful to look at the list of sub forums and find the one that best applies to the thread you are creating, so that the moderators don't have to move it for you. This works to your benefit. If your thread is in the wrong place, it may be missed by members who may be able to answer your question and once moved, it will automatically be placed in chronological order in its correct sub forum , which could mean it will appear further down the list than if it had been put in the right place right off the bat.