You have a map and compass. You shoot an azimuth to each illumination round (that is, measure the angle). You know where the illumination rounds are bursting, and from each you plot the back azimuth.
For example, suppose one bursts due South from you. From the point on the map where it burst, you draw a line going North. Another one bursts due West. From that point, you draw a line going due East. A third one bursts Southeast of you. You draw a line from that point going Northwest.
The three lines will intersect at a point -- and that's where you are.