Englishfor English speakers
A is used when the following word could be any of a certain type.
Compare "A book I saw on the shelf" and "The book I gave you yesterday".
A is the first letter of the alphabet.
The letter "a" comes before "b".
In some schools, an A is a very high grade.
Ron got an A on his earth science test.
If something is little, its size is not big.
I just ate a tiny little piece of the cake.
A little while, distance, etc. is not long.
Could you just wait a little while more?
A little person or animal is young.
Two little boys were fighting on the playground.
Little money, room, help, etc. is a small amount of it; not much.
They understood little or no French.
He was busy and had little time for children.
Try to spend as little of your money as possible.
We saw little of her after the first day.
Little is known about the problem.
The building was destroyed leaving little more than rock and glass.
She's a quiet person with little to say about these things.
This has little to do with him and a lot to do with you.
We saved what little was left.
A castle is a large, strong building used to protect the people inside.
In the Middle Ages, castles were used to protect the king and queen.
In chess, the castle is another name for the rook.
In chess, to castle is to take a turn that involves both the rook and the king moving at once.
I was going to win if he hadn't decided to castle.