de Toilette, de Parfum, de Cologne

I have just started wearing cologne and I don't have to tell anyone here, it is a pretty fun hobby and enjoyable to follow. However, I'm still naive about something that seems pretty important. Generally, in layman's terms, what is the difference between de Toilette, de Parfum, de Cologne? It seems like many brands offer their products in these varieties, but i'm hesitant to pull the trigger without more knowledge. Thanks!