The prologue serves as a tutorial on how to play. While there's no combat threat or time limit, it's still possible to get injured if you run into a visible hazard. The scene starts in what is quickly discovered to be the Croft Manor.
The first tunnel is simple - move ahead through the corridor. You may need to jump around the corner, and you will eventually reach a ledge that you have to grab and pull yourself up. You will find an open control box, which you can interact with to open the door.
The door leads to a circular room that's partially collapsed. Dive under the debris, and climb up on the other side. Use the grapple on the door ahead and pull the door down.
Past the door is a collapsed corridor with has a health pack. This section involves thin ledges where you climb with your hands. Head to the outcropping on the left, and jump onto the right wall to catch onto the ledge. Shimmy to the left, and jump to a ledge above. Continue left, drop down one ledge, and jump back onto the reachable floor.
A large box ahead needs to be pushed against the far corner against the flaming debris. Climb on the box, and shimmy against the ledge on the left to get across the burning debris. The end of the corridor collapses, but you can jump across the gap to reach the main hall.
At the main hall, you will need to use a grapple and swing across the stairs on the left. This lets you reach a gap on the other side of the room, where you can safely reach the ground. The prologue ends with a cutscene where Lara gets attacked by her supposed friend.