.

Save to your computer, make a project, load it.

if it's your project save it as a copy, otherwise save to your computer and load it. stealing projects is against the guidelines though

if you want to duplicate your own project:
inside the project editor you have a menu at the top. click “file”, then click “save as a copy”.

if you want to save someone else's project to your “my stuff”:
you can click “remix”.
or you can click “save to your computer”, open a new project, and click “load from your computer” (those options are all under “file”).
keep in mind that sharing a direct copy of someone else's project without changing anything is against the community guidelines, and so is sharing someone else's thing without giving credit.

Thank you very much !!!