Humankind is a great strategy game, and while you can definitely play with the AI, you can also play with your friends. You can play with multiple friends in Humankind and you can either host a game or join a game created by your friends.
To play multiplayer with your friends, all you have to do is go to the multiplayer tab in the main menu. This opens the multiplayer menu where you will see a list of games in progress. From there, you can either create a game or search for your friend's game with their lobby ID.
Related: How To Fix Failed To Join Multiplayer Game Error In Humankind
When you create the game, you have several options that you can adjust and choose. You can select the number of players who will participate in the game and each player can choose their avatar. You can change the size of the map as well as the type of map generation it will have. Other options include game pacing which controls the number of rounds and AI difficulty. You can also choose from pre-made maps if you have one you like.
Humanity also offers cross games. This is only for Steam and Xbox on PC. Google Stadia players will not be able to play with those on Steam or Xbox.
For more information on Humanity, check out What It Is and How to Perform Humanity Deeds and How to Improve Stability and Stop a Humanity Uprising on Pro Game Guides.