How to invite team members to collaborate?

You can invite users to the team by sending them an email invitation in the Team and resources section in the Account settings.

Also, you can invite users to a particular project by sending them an email invitation in the People tab of the given project. 

Here's a short video tutorial on how to add users:

You can configure rights and roles for the invited people upon invitation or afterwards. Once they accept the invitation and sign up, you can set personal calendars, assign tasks, and start collaborating on the project with these users.