I second not using a hobby knife to sculpt fur. A wet tooth pick will work, but I really would recommend getting a basic sculpting set these are what I use and I'm quite happy with them.
https://www.amazon.com/dp/B07PVBRQS1/ref=cm_sw_r_cp_apa_i_Bx6.FbJ520GPD
Also to practice you can totally use some blue-tac (or whatever you call it) to play around with some different textures without having a time limit or worrying about not liking your end product. It's sticky like fresh green stuff is, and it's also reusable! It's also great for when you want to pose a model for kitbashing.