no worries ! ill try and explain it in steps.
1. download the mini mob pack texture and set it to the version you want it to be in.
2. find the file u just downloaded and copy it
3. open up that version of minecraft
4. once ur in the home screen click options
5. click open resource packs
6. click open resource pack folder
7. paste the file u copied earlier into there
8. then click done and go back to the main screen. this needs to be done to sort of reset the texture pack folder
9. open back up resource packs
10. find the texture u downloaded and click the arrow.
11. click done and play the world normally! it should be all good!

if you wanna add multiple mobs into the game u can do the same thing for each mob i think. hope that works!

thank u <3
(: