Your bus will make scheduled stops throughout your journey so that you (and your driver) can get off the bus and have a break. Your itinerary will give you all the details.
Here are the different types of rest stops:
A quick break (around 15 minutes) to stretch your legs, use the restroom (if there's one at the stop), or have a smoke break. Rest stops are at designated rest areas along highways, places like truck stops and service centers, or a Greyhound station.
Usually around 30 minutes - enough time to get a meal from a fast food restaurant along the route. As the name suggests, this stop is somewhere that definitely has food.
A longer break at a Greyhound station (or another partner station on your route) while your driver takes the bus to be serviced and cleaned. You can use the station facilities and have a proper break, then a driver will bring the bus back for you to re-board. (Remember to take your carry-on baggage off the bus when you stop for a layover).
When you need to get off one bus and onto another, we'll stop at a Greyhound station (or, occasionally, another partner station) for your transfer. The time you'll wait depends on the schedule you choose. You'll need to take your under the bus baggage with you to the next bus too.