When you view a forum section (such as Forums (the big gold button), then Pre-University Math (the big blue ribbons), then Pre-Calculus (the things with the "blue pi diamonds" to the left), for example), in the upper left you should see a large-ish orange/brown button that says +Post New Thread. That button starts you on your way.
You most certainly may post questions...our primary goal is for people to post questions and to get timely and knowledgeable help.
First, you want to decide which of our subforums is the best fit for your question. Suppose you have a question regarding trigonometry. You would enter our Trigonometry subforum and there you will see the "Post New Thread" button above the existing threads (I have drawn an arrow to it).
Just click that button, and you will be taken to a form in which you can post your thread. Give the thread a brief but descriptive title...this title should indicate the nature of the problem. For example, suppose your problem involves the Law of Cosines, then you could use the title "Applying the Law of Cosines."
Then in the large text box beneath our toolbar, post the body of your post...this is where you post your question, and what you have tried and where you are stuck. When you are finished, the click the "Submit New Thread" button below and to the right of the post box.
Then one of our helpers will be along shortly to offer help. That's all there is too it.