I got into music and audio production at a time when audio editing was going digital starting with early samplers so I never did edit with a razor blade and splicing tape. However, I have spoken to many engineers who have.
Nowadays, the thought of editing in this way is alien to most people, however, this was the way it had to be done at one time. Imagine the amount of time it must have taken to edit or remix a song.
The process involved the audio engineer physically locating the point where a cut was required, before precisely cutting out that section of audio with a razor blade and cutting block. It was then rearranged and stuck back together using splicing tape (posh sticky tape). There was no cut and paste and no undo function.
This video illustrates it very well. At the start, you can see the splices, however, you can only appreciate the true art of this when the tape is played at normal speed. Enjoy 🙂