Short answer
HubSpot's KB: open the call remote from the top bar; the call window must stay open during calls. Paid Professional and Enterprise accounts need an assigned Sales or Service seat. Calling minutes depend on your subscription, and you're alerted near the limit.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Outcomes and logging rules are set separately in call settings.
3. Related
Phone number types and the call index.