Short answer
HubSpot's KB: from the add-in, set your log and track defaults and open integration settings. Use Customize Toolbar to pin HubSpot Sales. Super Admins set which associated records emails log to.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Desktop add-in users follow a separate settings article.
3. Related
Add-in sales tools and troubleshooting.