Can someone explain Lent to me?

Okay, I know the basics of it, but otherwise, I really don't get it. I was baptized Catholic but I went to an Evangelical church when I was young, and now we don't ever go. I've gone a couple times but I've felt so out of place. But my boyfriend is pretty into the church and I just want to know what Lent and Fat Tuesday, etc. is all about...