On the Manage - Members page, you can access the following functionalities:

To invite a new member, click on the + INVITE USER... button located in the upper right corner of the member list screen, enter the email of the user and set the username and role for the member from the pop-up window, then click INVITE button, an invite email will be sent to the user's email you put.

To access the actions for managing a member, click on the vertical ellipses symbol located at the end of the list row.

Be advised that only members with Team Administrator can invite, edit, and delete other members, for the detailed options of assignable roles, check the Security | Permissions page.

Also, be advised that creating new API Keys for accessing builder API is accessible from the user's profile blade by clicking the logged-in user's avatar, not from the Manage - members page.