1) download a texture pack. There are alot of great free textures on sai but this is a good starter pack ( Don't worry, it's safe.) It comes with these textures
2) open up the folder in which your texture pack was downloaded into. On my computer it will be in your downloads and be a zipped folder named sai-eng-pack-1.1.0
it will have a folder inside it called 'sai-pack' and inside that folder will be multiple other folders. It should go in order like this
we will only be using the items in bold.
3) Open up the folder called 'brushtex' and highlight and copy all of the items in