If you're a team owner in Streak, you can add users from the Teams page. Adding somebody to your team gives them access to pipelines shared within that team.
Once you’ve navigated to your Teams page:
Click the Streak menu item in Gmail's top bar.
Select the Manage Billing and Teams icon.
To the right of Members, select "Add/Remove Team Members."
This will open a new window with your current team displayed on the left side and your future team on the right.
Enter their name or email address into the field at the bottom of the right side and click the Add button.
Click the Continue button.
Confirm and click "Save Changes"
Once you’ve added the new teammate, they’ll need to download the Streak extension in their inbox. Upon adding them, they’ll receive an invitation to join your Streak team at the top of their inbox. To manage the pipelines you want this teammate to have access to, modify their permissions inside each pipeline.