What's a c3p file? A Construct 3 project, by any chance? Those can't be played by other people. You need to export the game first.
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Well, if you can't figure it out, ask in General Development. But the export command shouldn't be hard to find, it's pretty important.
However, this page from the Construct 3 manual says the export option is under Menu->Project. I just tried it online, and it's there.