There aren't really any videos specifically for skinning but there are videos for learning After Effects or Photoshop or whatever you want to use for creating animations, just keep in mind that the program you're using should be able to export as a png sequence (since that's how osu! reads animations, as RockRoller said), else you might have a hard time separating the frames.
McCreetard wrote:How can I do that? I have seen people saying After Effects but I've never tried any..Are there any specific vids that help on this particular topic? Like skinning or how to use a program to skin or so so..
If YouTube isn't enough you can also join the Discord servers below and ask for help.
Hope this helped.