Let's is a contraction of Let Us ...
EXAMPLE ~
Let's go get some ice cream. (Let us go get some ice cream. They mean the same thing.)
the answer is......... How do you use the word lets in a sentence?
lets get right to the investigation
lets sit on the bench
Lets go downstairs!
This is a stupid question. it is not even a sentence.
So- you are asking when to use 'when' in a sentence. When you are asking how to use when in a question, you are already using when in a sentence, because a question actually is a sentence. I like to use when in a sentence whenever I like.
You can post a question to the internet about how to use it in a sentence.
If your question starts with the words, 'who, why , what, when, where and how, your sentence will require a question mark
lets stop at the heliport first before lunch
Lets go find the definition to impression?
You use a question mark (?) as the punctuation after the sentence or question you are asking.
How do you use purple in a sentence! You answered your own question!