If someone is nominated, it means they are chosen to be in a competition or for a job.
Being nominated is usually a good thing because it means someone thinks you are good enough for something.
Examples:
She was nominated for the best student award.
They nominated him to be the team captain.
The teacher nominated me for the class president.
I was nominated for the best cookie maker in the family!
He was nominated for the fastest runner in the world.
The cat was nominated for the best sleeper in the house.