Inviting teammates is very easy. At the moment, you must be an Admin within Windmill to invite others.
As an Admin, navigate to the Employees tab, and you'll see a list of all users available in your system. This list is pulled in from connections made to Google, Slack and any other system you have connected.
From this list, you can invite managers or team members to Windmill by selecting the box next to their name, and selecting "invite".
If you don't see someone listed there, you can add them manually by pressing "Add Employee" on the top right of the screen.
When adding employees, there are two different access tiers, learn more about them here.