A file is something that you can put papers in.
If something is high, it means that it is tall.
If you guide someone, it means that you show them where they need to go.
If something hurts, it means that it is giving you pain.
We use instead when we want to say that something is replacing another thing.
A lock is something that keeps a door or window closed, so that people can’t open it.
A key is something that we use to open a door.
We use main when we want to say that something is the most important.
Your mind is the part of you that thinks and feels.
If you do something once, it means that you do it one time.