Two heads are better than one! If you want other people to also work on your project, you only need to select the project from the dropdown menu on the top left of the header bar and click on the team icon.
A form pops up prompting you to enter comma separated emails of your team members. Do that and click Invite. Each team member will receive an invitation email. They will have access to the project once they accept the invitation.
Now that you have successfully created your project and invited your friends, you might be wondering what your next steps might be from here on.