There are many English expressions that can be used to make suggestions. Two such expressions are:
Let's (do something.)
Why don't (we do something?)
These two expressions are used to make suggestions for activities that can be done with another person.
Each use verbs in the simple present form, but the action is always in the future.
Look at the following sentences.
Let's go to the movies.
Why don't we go to a movie?
Let's go to the movies next Saturday.
Why don't we go to the movies next Saturday.
In sentences 1 and 2, the person making the suggestion
wants to go to the movies now, at the time the sentence was spoken.
In sentences 3 and 4 the person speaking is trying to set a date to
go to the movies at some future time, (next Saturday).
Let's look at some more examples.
A: I'm bored. What should we do this afternoon?
B: I have an idea.
What's your idea?
Let's go try out that new restaurant downtown.
That's a good idea. After we eat, we can go see a movie.
A. It's cold outside. Why don't we go ice skating?
B: No, thanks. I just want to stay home. Let's build fire and make hot chocolate, instead.
Hmmm.. I love hot chocolate.
Let's = let us, but is not usually used in the non-contractive form unless the speaker is wants to be very formal.
People also use Why don't (you do something.) to make friendly suggestions, or to give friendly advice.
A: I'm tired.
B: Why don't you take a nap.
C: That's a good idea. I think I will.
Note: You can not use you with let's.
Incorrect: * Let's you take a nap.