Pathfinder is the first mission of Call of Duty. When you start the mission you will have landed in a field. Move up the field and you'll see a German taking a piss. Kill him and advance ahead. If you get hurt, then go to the house to the right where there is a 10% health. Follow the path to the right, you should see a dead American hanging from tree. This is in fact Sgt. Heath, who did not make the landing. Pick up the glowing leg bag and the M1 Garand if you want to use it. It is stronger than the carbine you start out with, but you can't reload with it until the whole clip is finished.
You should see a bunker ahead on the path. Inside are two Germans playing a board game. They don't know you're there, so kill them and fin the radio link just in front of the bunker. In the bunker to the left is the exit. Leave the bunker and set up the link. Now go to the second brick wall (where you were) and wait there until your buddies arrive. When the building in front of you explodes, it will be crawling with Germans, one of which has a machine gun. Shoot the machine gunner. When your allies begin to move, follow. One will kick open the house door. Follow your allies through the house, and up the stairs. When you reach the exit of house one, to the right is a German, kill him any way you want. The game will tell you to use a grenade, but it doesn't matter how you do it.
Once you leave the first house, you'll be in a tight space. Stay behind cover and use your Thompson. Also know that when you're halfway to the second house, the house window will pop open and a Jerry with an MP40 will attack you. When you kill him and the 4 or 5 other Germans, move on into the second house. Again a tight area, so reload your Tommy gun and get ready. When you go in the house, a stairway to the right will hold a German, kill him. When you get to the main hall, a German lorry will drop off 3 or 4 Germans. Kill them. When you leave the house, watch out! Most of the time (for some reason), a German will be hiding behind the doorway. Then you should see Capt. Foley from the training, follow him down the trench and you're done.