You can create content from two tabs on the users view:
- "OVERALL" tab: here you have the options "Start a discussion" if you want to create a forum, and "Post a blog" if you want to create a blog.
- "FORUMS" tab: there you can find a form called "New message", where you can add all the content.
Once you click on "Start a discussion" or enter the "FORUMS" tab, the form you have to complete is nearly the same.
You can choose the category, if empty it would be classified in "All posts", and also the tag to categorise the content.
Remember that if you want to create a new category you should go to the admin panel, to the "Manage forums" tab and create a new one there.
To create a new tag, you can do it from that form by clicking in "Add tags" → "Create new tag", or by the admin panel in the "Tags" tab.
Once the category and the tags are selected, just enter the subject and your message. Click on "Publish" to save it and make it visible.