You can unlock slimefun items in the sf guide that you can get by doing... /sf guide

There different sorts of items you can unlock them with xp. If you dont have an item unlocked and try to use it you will get the msg saying: "not enough knowledge to use this" then you need to unlock it in the sf guide! Btw I suggest using the /vote xp for that! Gl on your sf journey! Will be hard in the beginninf but youre going to be able to make some awesome stuff in the future!