To Lie Down
When you are tired, you go to bed and lie down.
e.g. I have been working all day and I am very tired. I am going to lie down for an hour.
To Lay Down
When you put something down on the floor, or on the table, you can say that you are going to ‘lay it down’.
e.g. I’m tired of reading so I’m going to lay my book down on the table and watch tv instead.
e.g. Please stop playing my guitar and lay it down in the guitar case.
To Tell a Lie
If you don’t tell the truth, then you are telling a lie. A “lie” is the opposite of “the truth”.
e.g. John told me that he used to play football for Manchester United. It can’t be true, he must be telling me a lie.
“A Lie” = Noun
“To Lie” = Verb