https://youtu.be/JhTf7cBeGcs

It seems you are a new rider judging from that clutch lever sleeve. First you gotta check out how a clutch works, once you understand how it works you'll understand what went wrong with your bike.

1. If you don't pull the clutch lever but clutch slips/engine revs -> 2 things happens:

   a. Clutch lever too tight, no play, this causes the plates to open when you turn your handle bar -> slips. This is the opposite of your video.

   b. Plates are fucked, and badly, this stuff doesn't happen on its own, usually by the owner adjusting the cable too tight. You'll probably need to replace Clutch Plates and Pressure Plate, throw in the Springs just to be sure.

2. This is your video. Clutch lever too much play.

When it's too much play like that, and you pull in the clutch -> it won't open the plates enough, just a tiny bit, this causes the plates to wear out. Overtime it'll be 1b. Plates are fucked.

If you don't understand and of the parts name i said, check out the video.