To unlock the Play the Objective trophy in Battlefield 1, you will need to complete 25 squad orders in multiplayer games.
Only the squad leader can set orders, so your best bet it to create your own squad when you join a new game so that you are always the squad leader.
In a multiplayer game, press
over objectives such as captures points in conquest mode. Once an objective has been successfully captured if you are attacking or defended if you are defending, the squad order will be successfully completed. You'll see a notification on the screen to confirm and will also receive some bonus XP points.
Do this 25 times in total and the trophy will unlock.