After downloading the game file in the PGN format, open the file with any text editor (e.g. Notepad in Windows) and check it's not empty. Your friend can do the same after receiving the file. If the file looks fine, it's just a matter of opening it with the right chess application.
pgn files

You can also dl something like Winboard (HERE). It's an interface/viewer. Input the moves on the board, then you can save the file (it will be a pgn) or copy [Ctrl+C] the game and paste it into notepad or any text editor, or just into an email or message. it will be in pgn format that can be copied and pasted [Ctrl+P] anywhere.... in the chess.com viewer or even into Winboard if your friend also has it.
To make a pgn by hand, you have to follow the correct formatting for it to work. If you don't know the correct formatting, search pgn in google - or - get an existing pgn file, delete the moves and type in your own, then change the data (player's names, venue, date, etc ) in the header to reflect what you want. Winboard is a lot easier.
Is it possible to construct a pgn file from a game you play with a friend that's not online? I played at my house with a friend using real chess pieces. Then I loaded the moves that I had written down using the chess.com pgn format . Then, I downloaded the game and sent the file in an email to him. But when he opened the file, it was empty.