Can someone help with making bukkit plugins on a Mac

[reuben_1]

Hi there,
I would like to make a basic plugin with a /hello command that when types outputs "Hello, user!" or there minecraft user name
I have done all the code, and I have a problem of which the server says:
[16:02:10 ERROR]: Could not load 'plugins/GreetingsPlugin.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: Cannot find main class `me.robbierobster987.Greetings'
Please ask any questions so you can help me, I would really like to get this solved so I can make more plugins, btw do you have a tut on making plugins 1.7.10 for mac?

[reuben_1]

btw I am 13, new to java programming

[stultuske]

a plugin for what, exactly?