First, go to the forum. (Learn How at this topic: Basic Navigation
Click the Actions menu on the right side of the banner. Then click Discussion.
However, on the Content page in many forums there is an easier way. Just ask a question.
When you create the topic, remember to identify whether it is a discussion or a question.
You can also add tags to your discussion, so you or other people can find it easily by searching, without having to navigate.