is there a way to upload videos to the system and then have other users to watch it?

I think you can accomplish this by passing the in-Appian URL of the uploaded video file, i.e. perhaps by using "document(ri!videoFileId, "url")".  I'll see if I can confirm in my community site.

Edit: tried it out and it works fine.

a!videoField(
  label: "Video",
  labelPosition: "ABOVE",
  videos: {
    a!webVideo(
      source: document(cons!MS_TEST_VIDEO, "url")
    )
  }
)