minecraft.novylen.net

I've heard about plug-ins, like shop plug-ins, but I don't know how or where to get them. Could somebody help me?

You do know those are server plug ins right? for if you own a server like Novylen

If you type /plugins in-game, it will give you a list of the plugins running on this server. You can then google them to find out what they do and how to use em, or try typing /pluginname help. That often gives info. As for client side plug ins, I don't know if there are many that function with our multiplayer aside from texture packs.