Local Multiplayer means that the game can be played offline, and you can played it either as a co-op game (a.k.a your other player is helping you), or as your opponent.

If you're playing the PC version (whether you got it for free from the Epic Games Store or paid for it on Steam), you can grab a friend and play online in the Parsec Arcade. With Parsec, it's a cinch to start playing with your friends online.