It essentially means that if you've been hurt or harmed by something once, you'll be more hesitant to do it again, even if the situation seems different.
Here are some examples of how it might be used:
* "After getting scammed by a fake online store, John is now once bitten twice shy about buying things online."
* "She's been burned by love before, so she's once bitten twice shy about opening up to someone new."
The proverb highlights the human tendency to learn from negative experiences and avoid repeating mistakes.