Custom Plugins?

So I have been thinking lately about available server plugins. Not much to choose from, right? I was wishing i could just think of an idea and make that plugin. I have taken a few coding classes, but they weren't very helpful. Also, I don't even know what type of files to make or how to combine them into a jar file. I want to make my server completely custom, made by me, not a bunch of other people's plugins that are confusing a sometimes annoying. If anyone knows any website or class i could take to learn how to design plugins, please recommend it to me.