I really hope it works to put links in here...
It's the site from a carnival society, they have explanations in english how the "fifth season" is celebrated in my part of Germany. They celebrate a bit different farther south.
The essence is to have parades through the streets, dress up in silly costumes (my fiancee went as Emily Howard from the BBC comedy Little Britain, I went as a gentlemen to the parade. To the session he wore a french frie costume and I was a cat), catch lots of sweets thrown by the parade people and party afterwards. Some go to sessions where speeches are hold, they are in verses, about politicians and stars what they did wrong, but comical. it's kind of difficult to describe. They are able to talk about people like you'd never be able to face to face.
Typical is some kind of formation dancers, music, ...
And it's great fun!
The session we went to was a small one from the local shooting club. Their speeches weren't so much about politicians but our neighbours and whatever funny happened around the village.
For example, it was about holiday camp where some guy confused his toothpaste with his suntan lotion in the dark and only found out after he already put the brush into his mouth.
The cousin of my fiancee was mentioned as well, he went to see a football match without a description how to get there and missed the first goal because he was 40 minutes late. He missed the second while getting himself a beer, the third because after drinking he needed to go somewhere...

Well... maybe you better just look up Karnevalsumzug or Karnevalssitzung on Youtube to get a picture of the parades and stuff. I don't know if any of the bigger ones are on there, but watch out for Koeln or Duesseldorf

The roots of Karneval are somewhere in the mist of time when the old germans decided that all the spirits that crept closer during winter had to be shooed away. Right now it's more like a last minute party before lent
And I still don't know what I'm doing this year. Usually it's no alcohol and no fast food for me during lent, as it's too hard for me to stop eating meat.