Project members in the list not created by me

Hi all.
Sorry for my poor English, hope I’ll be able to explain clearly my question.
I just started using gitlab free version online and created an empty project.
When i try to add a new user to the project, clicking in the field labelled People I see a list of names (users i guess) that I don’t know nor i never added before…after all mine is a new account with a new project.
Are those users created by default?
Do they have some kind of access to my project or online space?
Can I delete them?
Thanks for your help.