If you would like your students to participate in class discussions, the Forum option on Moodle is your best choice. This allows for asynchronous discussion, while still putting a deadline in place for a discussion end point. You can watch a short video on creating a forum, as well as a video on adding a discussion post to your forum.
To add a forum to your course, you will first need to make sure editing is turned on under the Administration menu on Moodle.
Once editing is turned on, you'll add a forum for your students by clicking "Add assignment or resource" for the topic or week it's assigned.
From the pop-up, you will select "Forum." As you can see from the description, there are a lot of ways to use the form function, from making a Q&A to having formal weekly discussions.
There are other options to play around with, but Availability will be the most relevant. If you use the Groups function, you can also assign specific forums to specific groups. You can edit subscription status to ensure students get updates, or disable to it to keep students from being inundated with emails. When you've edited the settings that are relevant to you, click "Save and Display."