From your 'My Hub' page (please see below)
If you go to the 'Menu' icon in the top right...
then select 'Groups' from the options
This will then show any groups you have created
Click the 'Client' tab from the 5 options at the top of your page.
And by clicking 'Create Client Group' at the bottom of your screen
You will be able to create a Client group
Once created you can simply select the 3 horizontal grey dots in the top right and click 'Preview' where you can then add any of your clients via the 'Clients' tab.
Then select any of the tabs at the top of the page to add Forms, Workouts, Nutrition Plans, Programs etc as well as Workouts and Nutrition Plan groups.