"While" expresses that something is happening at the same time as something else; two things are happening at once.
1. She likes to work on her laptop while she's on vacation.
2. This dog is sitting patiently and waiting while her owner puts on her leash.
3. While he's at work, he wears a hardhat.
4. This police officer wears a uniform while he's on duty.
Next: Lesson Twenty