If you wish other users to view your project, you will need to 'invite' them. The user who you wish to share the project with will need to have an account on the Definition Center, unless you have assigned it as a Public Project.
To share the project, click on the Project Name link, which will take you to the project detail screen. Click on the Invite People link and start typing the name of the person you wish to share the project with.
To assign a group of users, type the name of the group, and all members of the group will be granted permissions on the project. See this article on how to manage group members.
View/comment - will allow the user to simulate and comment on the project. This permission will also allow the user to manage requirements in Manager. They cannot edit the project.
Edit - set the permission to Edit if you want the user to be able to edit the project as well as view/comment. In order to edit a project, the user must be granted the Author role. This article provides further details on managing users.
Owner - similar settings to Edit, but will allow the user to delete the project.
Select the checkbox to send an email notification to the user. The invitee will receive an email notifying them they have been added to a project, their permission type, and a link to the project.