In order to share a course with clients, you must first create a group then assign the course to it. 

Step 1: Create a new groupGo to 'My Groups' then click on 'Create New Group'

Step 2: Under the Course tab, select a course to assign to the group 

Step 3: Once you finish setting up the group, click the "Copy Link" button to grab a client invitation link. This is the link that you will share with your client.

Note: You cannot share the course directly. It must be part of a group.

Related Articles:

What should I create first - a Group, Course, or Module?

How do I add modules to a Course?

I want to share modules with my clients - how do I give them access?