In the Fusion web client, navigate to the project you want to invite people to.
Optional: If you want to invite members to a specific folder in the project, navigate to that folder.
Click the Members and Permissions tab.

Click the Add or search members and groups box.

Select members from the drop-down list, or type in the names, email addresses, or groups of people you want to invite, separated by commas.
You can enter multiple names. If names match members of the hub, Fusion detects them and populates the box accordingly.
You can enter email addresses for people who are not already part of the hub. Invitations will be sent to these addresses.
To give access to everyone in the hub, select Everyone.
Click Add or press Enter to create a list of who will be invited.
Click a name in the list to open the Focus Panel on the right.

Under Directly applied role, select the permission level for the new member.
For information on how permission levels and security work, see Projects and folders.
Optional: If this is an individual, under Add to groups, select a group to add the person to.
For information on groups, see Work with groups in project folders.
Repeat the previous two steps for the other names in the list.
Once permission levels are assigned, the members are added to the project (or project folder, if you selected one in the first step).