I don't have any tutorial video. If you want to learn, there's plenty online tutorial that can help you. This is one of them https://www.youtube.com/watch?v=MFvsRvo_78Y Also
Also There's online community that can help you. Pixelation is the great place to start.
The pixelation is community for pixel artist. However, Tileset aren't necessary to be pixel art. You can for example create a tileset with digital painting or vector image.
If you want to make tiles you need to learn how to tiling, grid, etc. The youtube video that I mentioned before was my starting point. It explain how the tileset works and how to tiling them.
