Only members of your team assigned to the project can view and work on it.
When creating a new project, you can decide who is going to be working on it:
On the projects page, click on the Edit icon:
Under Team, select Click here to manage project users:
Toggle the switch to green next to the correct user to provide access to this project:
To change the project owner, select the Owner tab and toggle the switch to green next to the correct user:
Next help article: Activity feed and revision history →