Can you slow down a video in the video editor?

For example, if you create a video that is 100 FPS. 10 seconds long.
And we know that Youtube only allows 30 FPS.
Can you us the video editor to slow down 100fps to 30 fps.

In other words: stretch the video out in the video editor?

Yes, the video editor will bring in the clips as if 1 frame = 1 frame, so if your source video is 100fps, and you have your timeline set to 30fps, and the original footage is 1 second long, it will appear in the VSE to be 3.33333333 seconds in length.