How to add guests and users by email
There are two ways to add team members. You can either invite them by email as shown below or add them through your Slack integration.
Step 1. Team settings
Click on Team settings on the top-left menu. That will take you straight to Team members.
Step 2. Invite teammates
Click on Team members and then on Invite teammates.
Step 3. Add emails
On the pop-up that will appear, select the Role, select Email contacts and add their email addresses.
On the Team members page, you can identify the Login Type each user has. Email users can edit their profile settings once they are logged in.
Email users cannot share pages to Slack.
Learn more about roles here and about adding Slack team members here.