Are you attempting to lock a particular feature in place? Or remove camera shake while preserving the overall motion?
For the former, a few 2d point tracks (the regular Tracker node) will do. Run the track, then in the Operation tab, set the Operation to Match Move and the Merge to BG Only (note for BMD: Those controls are now even more confusing than they were when they were multi-buttons).
To remove shake from a 3d tracked camera, it's a bit more involved. Yes, you'll want the CameraTracker node, but it doesn't have built-in a way to designate supervised tracking points. You can mask out the moving people, but if you want a user track, you'll need to do a bit more. I haven't tried it yet, but there is now a script that can copy tracked points from Fusion's point Tracker to a CameraTracker node:
https://www.steakunderwater.com/wesuckl ... f=6&t=2602Once you have the track, you'll export the camera as described in the docs. Make a copy of that camera and smooth the path and rotations of the copy. Give it a recognizable name to make it easier to identify. Plug the new camera into the 3d scene. In the Renderer3D node, change the Camera to your new camera.
The original camera has a visible image plane. All of the bumps and shakes are present in the image plane, but the camera projecting it is mimicking them. The result is that the image itself is actually stable in the context of the 3d scene, and by reshooting it with a smoothed camera, you get the stabilized picture.