How to use feed the beast in minecraft?

I downloaded the feed the beast mod launcher and I created a profile, but every time I click on Launch button, it says "invalid username or password". Why does it tell me that? How do I use it correctly and how do I install/use the mods?

Jacob Elder

You select the modpack you want to play, and after putting in your Minecraft username and password, click launch. Are you using a valid Minecraft account to play? The first time I used it I got the same problem and realized I had typed my password incorrectly.

Vaneetra