You can invite your client into their business from the Settings and Access menu (at the top of the screen).
This will be as a 'user'. The Role you choose will depend on what you want your client to see:
Admin Role - gives clients access to their 7 Key Numbers, their Action Plan and their tasks.
Standard Role - gives access to their Action Plan and Tasks.
Verifier Role - is to only verify data in the client Structured Dataroom, they do not get access to anything else.