how do you share files between two mac's?

Open the Sharing pane of System Preferences on one, turn on File Sharing, and use the Connect to Server command in the Finder's Go menu on the other.

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You can either use AirDrop, or depending on what type of file it is it might also be possible to email it to your other Mac. The only thing you have to consider is that if it's a file larger than 25MB it will use some cloud storage space.