Follow the following steps to create groups and to assign courses to groups.

Step 1: 

Login to your LMS domain

Step 2: 

Navigate to List Group under Accounts and settings.

Step 3:

Click on Add Group.

Step 4:

Enter Group name and Group description and click on Save.

Step 5:

Click on Add users in the option column.

Step 6:

Select the users you need to add in the group.

Step 7:

Navigate to Course.

Step 8: 

Click on more on the course that you need to add to the group and select Assign user group.

Step 9:

Select the user group to assign the course and click on save.