How does proper flossing protect your teeth from getting cavity? 

Normally, teeth come into contact with each other at a point (contact point). However, this is merely a kissing contact (light contact); teeth are not attached, so when food particles get there, it is best to remove them before they cause tooth decay or gum problems (e.g. inflammation and bleeding) for that matter. So, get on with your flossing, just make sure that you do it properly.

Use dental floss or other interdental cleaners, such as special picks, interproximal brushes or sticks at least twice a day. Using these can help loosen and remove plaque and food particles from the spaces between your teeth, where your toothbrush cannot reach.
As you do with dental brushing, use a gentle touch when cleaning between your teeth. Remember: Flossing is NO substitute for brushing and vice-versa.

Feel free to ask me or your dental hygienist to help you develop a comfortable and effective technique.