Sometimes you'll want to collaborate with people who aren't in your team’s organization. A lot of times you'll be doing that in email, but if you want to collaborate with them in Teams, you can add them as a guest.
Note: Before guests can join a team, an admin must enable guest access in Teams. If you can't add a guest, check with your admin.
Guests must have an Office 365 work or school account. If the guest doesn’t yet have a Microsoft account associated with their email address, they will be directed to create one for free.
To add a guest to your team in Teams:
Select Teams and go to the team in your team list.
Select More options > Add member.
Enter the guest's email address. Anyone with a business or consumer email account, such as Outlook, Gmail, or others, can join your team as a guest.
Note: If you receive a "We didn't find any matches" error while trying to add a guest, your organization doesn't allow guests.
Add your guest's name. Select Edit guest information and type a friendly name for them. Be sure to take the time to do this now—you’ll need the help of an IT admin to do it later.
Click Add. Guests will receive a welcome email invitation that includes some information about joining Teams and what the guest experience is like.
Now that all that's done, the next thing you're going to do is set guest permissions.