World War Brothers WW2 is a fantastic first-person shooter game with a large selection of classic weapons and battlegrounds.
The concept is straightforward: you go to a map, like Omaha Beach, and you have to shoot enemy soldiers to win the war. If you can make it to the end and kill more players than them, you go up the leaderboards.
In between games, you can purchase new weapons from the store and receive surprise boxes that you can open and utilize to your advantage to obtain the appropriate equipment and armament. Move with WASD, leap with the spacebar, aim and shoot with the mouse, and open the shop with B.
Have fun and good luck!