“Pop the hood, will you?”
Your son's car has some kind of problem in the engine. You know a little about cars, so you're going to try to fix it. You want him to open the front of the car so you can look at the engine.
Pop the hood, will you?
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The "hood" of a car is the flat part in front that covers the engine. To "pop the hood" means to open it up.
You can also "pop" the trunk of a car:
Hey, can you pop the trunk?
Of course, "open the hood" and "open the trunk" are both OK, but "pop" is more casual and conversational-sounding.
Ask "will you?" at the end of a small request in very casual conversation. For example:
Pass me the salt, will you?
Give me a hand with these boxes, will you?