Once both players are on the 1st tee the game will automatically find your friend(s) & add them to the round.
If their status is "Live" - you're good to go.
You will see your friends ghost ball & John (the announcer) will keep you up to date with their progress. But, if you want to view the other players strokes & ball cam you need to
enable "turn based" from the pause options.
If the game fails to find your friend(s) automatically there is a way to add them from the pause options.
Select "active friends" then from the list that opens ... highlight (select) their name & "add player to game" (remember to "enable turn based" before backing out to the course screen).
*Note: to access the pause menu whilst in game using a controller press the "start button" usually located to the left of the A/B/X/Y buttons... sorry I don't know the keyboard/mouse path if your playing using that format.
Tip:- Allow the game a little time to find your friend(s) automatically as internet connection speed can be a factor. The same is true when waiting for your friend(s) to take their shots.
Hope this helps... I did it from memory so apologies in advance if anything is wrong.
Good luck.
Edit: Keep in mind it's turn based, so - you'll play first until somebody wins a hole and takes "the honours."