Inviting your clients means you create a connection between your account and their account. Your clients can take various actions and make certain requests along with getting perks for partnering with you.
Once invited they can access their "agent dashboard".
To invite, simply load your agent into the agent box on your Partner dashboard.
Click the handshake button and a popup will come up. It may have an email address in the bar already, however you can overwrite it. This will be the email that is attached to the account and also the email that sign up instructions are sent to.
And that's it! Your accounts are now linked and they are invited under you once they create their account using the link that was emailed to them.