If you are a company admin, find an Invite App Users link on your Management page.
If you are c group admin, find Invite App Users link in your top right corner menu.
Your user will get an email to join application
After following the link your user will see the registration form:
After filling this form the user will see the buttons to AppStore and Google Play to download application and receive an SMS with the code to log in the application.
You can also send the direct link to this registration form.