signs for "do"
what to do
did
don't
"?" for Yes/No questions
eliminate "do" for WH questions
do (spell “do” for a statement)

What to Do
What will you do?

Did
I did the homework. 

Not
I don’t understand. 

Yes/No Question
Do you like the food?

WH Question
What do you see?

Do
I will do this.