To Create a Cohort of a course, Go to Managed courses Page.
Under the course for which the cohort needs to be created, click on the Manage Cohorts icon.
In the course cohort page, on the right top corner, you will get Create cohort button. click on it.
This will open the cohort details page. Here Enter all the details : Name, start and end date, Maximum number of learner’s in the cohort, Invite code. You can also set Automatic approval.
Then, click on the save Cohort Button. Your cohort will be created.