Replying to What Frame Rate

What frame rate should I be using to film? I know 24 is for cinematic and 30 for tv but you can go all the way up to 240+ depending on the camera. It seems like higher is better for action sports cause it gives you a smoother shot?

What about the project’s frame rate? Say I have two clips, one shot at 30 fps and one at 60 fps. If I set my project frame rate to 30 what happens to the 60 fps shot? And vice versa.

Finally, slow motion. Obviously a shot at 30 fps is going to look choppy in slo mo. What about 60 fps. Or would 120-240 be ideal?

The biggest thing I don’t understand is how an editing software adjusts to incorporate clips with different frame rates into a project with a set frame rate? Does it get rid of half the frames of a 60 fps shot if the project is at 30 fps?