The skills plugin has 15 different skills to level up that provide unique abilities and stat increases
You can view all of your skills in game with /skills
Click on each one or type /skillname i.e. /farming to view information about each skill in game
You can level your skills up through various means listed in the experience bottle on each skill page in /skills as well as by acquiring skill experience books from crates which, when right clicked in the air, will give you experience for that specific skill.