From the main screen, click on [Resources][Discussion Forums].  You will be taken to a screen with different forums.  The T-SQL forum seems to be the most popular but take the time to scan the list to find the most appropriate forum.  Then, click on that forum and you will be taken to that forum.  Near the top of the window is a "button" to start a new thread... click on it and type your question.

Remember to include information about any tables you have (column names, datatype, etc) for the columns required to solve you problem.  Also, include some sample data and what you'd like the output to look like as well as a description of what process you'd like to follow to get to that output.