To configure, who can create and mangage projects, access the "Settings" section in the bottom left corner of the sidebar, then scroll down to the "Permissions" column on the right side of the screen. Configure if you want new projects to be public or private by default.
In addition to managing Projects settings, you can also manage who can create tasks in a particular projects. To manage this setting, go into "Projects" and then click "Edit" on the project you want to modify. Configure who can create tasks in the project. Flick the "Team" switch to make the project visible only to chosen members. You can also do all of this when creating a new project.
Guides - How to manage workspace users
Guides - How to change the default cost and billable rate