Hold the line in the dunes. Your slot guns shoot enemies in each lane during waves. Upgrade the wall, assign weapons, lay mines.
Flow: Play opens settings (base side + profile), then difficulty, then the shop before wave 1.
During waves, each slot gun fires at enemies in its lane automatically (you choose weapons and slots in the shop before the first wave and between waves). The shop opens first after you pick difficulty, then again after each wave you clear.
Rebuild your defenses and try again.