Locate Hadley's Hope | Mission 4: No Hope in Hadley's A: CM Guide

Follow the other marines. You won't run into any hostile units for the next several minutes, so you can lower your guard and stop looking over your shoulder. At the first fork in the road, choose whichever path suits you, they meet again a while later.

Continue exploring the planet's surface and a few moments later you'll reach the titular colony. As you make your way for the entrance to the complex, you'll receive new orders.