It's time to start fighting. You find out that your main objective is to clear enemies at the nearby camp, radio for supplies, and clear out the cave for the supply drop. That's basically what you will do. As soon as you make a step, a handful of enemies will come out. Thankfully, your allies are there to help and the enemies are behind trees. Just find one, bring your crosshairs to it, and fire. You will see a red bar if you are getting damage. If you are, immediately kill the soldier that's shooting you (he will be in the direction of the red bar. Remember to relax. These enemies shouldn't be too much. Move forward and do the same. You will have to mantle, but that is easy. Once the enemies are cleared out, go over to the orange colored mortar (you might have to wait for it to be set up first). Do what you did at training. Your target is the tower. Then go to the other mortar and do the same.
Now you will move forward and clear more enemies. Then there will be a resupply box to replenish your ammo. Move up, but slowly, because there is a land mine. When you see the hand, immediately stop moving and touch it.
Disarming a land mine may seem tricky at first. First touch the pins and drag them out one by one. Then turn the mine counteer-clockwise slowly and hold it when the red bar at the left is in the green area. If you let go while turning it, you will have to start over with that part. Then touch the mine, and remove it, and IMMEDIATELY touch the 4 items starting with the top one going CLOCKWISE. You only have 10 seconds for this! Finally, drag the 2 metals off but do not let them touch the materials to the sides, or it will blow up. Also remember to not let go until you have dragged them off screen.