Knowing how to navigate yourself on the battlefield is extremely important, especially during the exchange of fire. There's no enemies with red markers over their heads running around, so you'll have to use the available tools.
Most often you will be forced to use a compass. Members of your team will often use phrases such as "enemy, 200 meters, west" in both the single player missions and multiplayer. It is then best to use a compass, which is available by default under K. You can also see the "bearing" on your compass. Bearing is a set of numbers that are spaced apart at the edges of the compass. For example, if someone in your group says "enemy, bearing 250", then open the compass and turn it, so the red line is on the number 250.
Another element of navigation in the area is also the co-ordination of "grid". For example - the members of your group will use a phrase "enemy, grid 051035", when they'll spot an enemy at a certain location. In order to find out that location, you will have to open your map (M by default). You'll notice numbers on the left and the bottom side of the map. Grid co-ordination numbers always begin with the left side and then the bottom. From each number there is a line, so you need to look at a spot where the lines from the number 051 and 035 connect with each other - that is where the enemy is located.