Slimefun is a plugin which attempts to make vanilla minecraft, more akin to something like a modpack. It adds many small features such as electricity systems, Backpacks, specialty tools, talismans, jetpacks, multi-tools, and many more items. You can interact with this plugin as much as you wish and the server can be entirely vanilla if you don't care for it or you can just gain the items you care for and leave the rest.
It's best to take this plugin bit by bit and theres too many options to discuss here. If the plugin says "Multi-craft", that means you have to place the blocks as shown (For example: an enhanced crafting table is made by placing a workbench with a dispenser on top).