Hooded eyes have a fold of skin that droops over the eyelid crease. It mostly happens with age, but other people are born with eyes like these. Look at your eyes in a mirror. If you can barely see your eyelid then you have hooded eyes.
Hooded eyes make the eyes seem small. Your aim is to make the eyes appear bigger. Small eyes present the same problem, and have the same solution.
How to achieve it
The risk is that if you have to heavy an addition of extension lashes, it may only make the eyes seem even smaller. The best answer is to place the emphasis of the extension lashes on the middle of the eye, and also use a strong curl at that point. This should open up the eye.