If you have a question, the best way to use the forums is to search to see if your question has been answered before. A lot of people read the forums for weeks, months, sometimes even years before posting.
If you can't find the answer, ask your question. If you know the answer to somebody else's question, feel free to answer. There are lots of subforums to choose from to narrow down the area in which to ask your question.
Outside of questions, find an appropriate forum and show off your tank! Tell us about your recent build! Show off that great pic you got of your favorite fish or coral! Tell us about your trip SCUBA diving in the Caribbean!
It's a very open community and we're all crazy about saltwater. And some of us are just crazy in general. No shaming allowed! Welcome to the madness.