My friend sent a deck to me via email

My friend sent me a deck of his via gmail in a .akpg file format and I don’t know how to sync it up to my decks.

Download the file and import to Anki clicking on File > Import.

Were you able to import it? If you have AnkiMobile installed, you should get an option to open .apkg files in AnkiMobile when you try to ope them/use the share icon.