The helicopter in which you escaped after the last mission in brought down by the enemy's missile. You and your teammates survived. However, that's the end of good news. When you crashed, a hunt begun and you are the game.
At the beginning you only have a pistol, pick up a weapon (#65) that is lying next to the dead pilot - he won't need it anymore. Captain Price will give an order to move out of there. And that's a good decision as soon there will be hordes of enemy soldiers looking for survivors.
Follow the only path. According to your commander's order, hide under the bridge (#66), so that the helicopter can't spot you. You will get to some buildings. Wait for Price to open the door (#67), and get rid of the enemies patrolling the yard (#68). When it's safe, jump over the fence (#69) and keep going.
Hostile helicopter will show up again. Prone and wait (#70), until the helicopter passes you. Then run to the nearest building. Hide behind the wheel of hay (#71) and get ready to fight.
When enemy soldiers show up, they will try to smoke you out of the hide-out. Kill the soldiers running towards you and wait until one of your mates opens the hatch leading into a cellar (#72). As soon as you hear an order head into the building.
Despite what you may think, it's not safe there , so find the stairs (#73) and head up. Get to the front door. Kill the enemies that'll show up and go outside (#74).