You can allow students to create a new discussion by changing the course settings. Settings are available in the Discussions Page or the Course Settings Page.
Discussions Page Settings
In Course Navigation, click the Discussions link.
Open Settings Icon
Click the Settings icon to open Discussion settings.
Edit Discussion Settings
Make sure you mark the Create discussion topics checkbox.
Note: Unchecking this option will restrict students from creating their own Discussion posts. This permission affects posts in new discussion topics, discussion replies, and discussions within course groups.
You can also change the Discussions permissions in the Course Settings.
In Course Navigation, click the Settings link.
View Course Details
View Course Details.
Select More Options
Click the More Options link.
Allow Students to Create Discussion Topics
Make sure you mark the Let students create discussion topics checkbox . Once you have made the changes, click the Update Course Details button .