how to save files in Final cut pro ?

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FCP X saves your work automatically.

There is a Duplicate Project/Snapshot feature that basically allows you to version your work.

Any files used for Sharing go to a Shared file folder that is automatically emptied after FCP X is closed.

You can drag or copy them out of this folder before closing.

Libraries are auto backed up and go to your Movies folder.

Al

FCP X automatically saves as you go. In addition it creates backups of your working libraries every 15 minutes or so.

If you want to have copies of your projects use the Duplicate or Fuplicate as Snapshot commands.