So, I was thinking about how drones work, and I can't figure out how drones with propellers at the rear of the drone can still go forward. I'm not that experienced in aviation so if this is a basic question, I just didn't know the answer.
Yes, in fact airplanes with pusher propellers were flying before those with tractor propellers:
Photo Credit: Smithsonian Air & Space Magazine
Your Question: Can you put a propeller on the back of a plane, and have it go forward?
Yes, there are several airplane types that have rear engines. Here is an example:
Cessna 337: Source: https://www.flyingbulls.at/en/fleet/cessna-337-skymaster-push-pull
Here is another example: Piaggio P.180 Avanti
And another example: Convair B-36 Peacemaker
There are actually some planes that have this setup. Majority of prop driven airplanes use the pulling method, in which the propeller acts like a airfoil (wing) and the propeller itself generates lift which pulls the plane forward. This is also known as the tractor configuration.
But in this case you are talking about a pusher configuration. There are a few planes which have this configuration As seen below.
The Pusher configuration actually works just the same way as the tractor configuration. So the drone that you are referring to works no different from normal planes.
This website talks more about how propellers work. How propellers work
And this link talks about some of differences and pros and cons Pusher versus pulling propeller
To answer the question in your text (instead of the title):
Suppose you bought a used single-engine airplane with the propeller on the nose and fixed it up. Imagine starting up the engine, the prop spinning, blowing air backward, pulling the plane forward.
Now imagine you have bought the wrong engine. When you start it up, it runs in reverse, the prop spinning in the other direction. What happens? The prop blows air forward, pushing the plane backward.
Obviously this is useless as the plane is not designed to fly backward. You can't even taxi straight.
So you disconnect the plane from the engine, keeping the engine where it is, turn the plane around, and attach the tail to the engine. Now the engine and the plane agree about which direction they should go. You have invented the pusher prop.
Of course, if you want to get the thing to actually fly, you're going to make a lot of changes -- but none of those changes will involve changing the direction the engine is spinning, or changing the direction the plane is pointing.
Instead of spending years of wind tunnel and dangerous flight testing, you can
steal plagiarize copy most of those changes from other inventors. You want to look at the Rutan LongEZ, the Anderson Greenwood AG-14, and the Cessna 337 Skymaster, for example.
In every case, the engine is stuck onto the wrong end of the airplane, but that's OK, because the engine spins the wrong way.
EDIT: To help the OP better grasp the concept of how it's possible to put propellers on the back of a plane and help them grasp the concept of how drones with propellers on the back work, it may help just as an initial frame of reference to think of the placement of the propellers on planes as operating similarly, in basic principle, to the main two types of vehicles and cars on the road with regard to those that are driven using front-wheel drive versus rear-wheel drive driven vehicle.
Whereas most modern vehicles in the Western part of the world utilize a front-wheel drive setup that involves having the engine usually being installed in the front of the vehicle and is used to spin the front wheels, whereas the spinning force of the wheels pull the car forward.
Conversely, in a rear-wheel drive model vehicle, the engine is usually found in the back of the vehicle and otherwise is used to spin the rear wheel tires to push the car forward.
Both constructs have their advantages and disadvantages similarly to planes with those designed to have propellers in the front and those designed to have propellers in the back.
The propellers themselves play almost the same exact roles as the wheels on a car where power from the motor engine is used to rotate the propellers which exerts the necessary force of momentum to move forward. In this case, spinning the propeller blades force air to move in a particular direction that is generally coming out from "behind" or "under" the propellers if you looked at them from a top-down view. Others have answeres with links above to learn more about how propeller works but hopefully that helps remove any confusion that may have prevented an better understanding.
In previous posts, everyone provided great answers already explaining the difference in propeller systems and it was only in realizing how I had misperceived the reference to drones that I realized, maybe the OP has reached the same level of understanding that might seem like second nature to others and before diving in to the details of the physics and technical explanations on how propellers work, I thought it might help the OP better grasp the general concept and ideas rather than what was previously suggested and written below, but otherwise the above edit was added while below is kept simply for posterity.
Although I would've elected to post this as a comment and an answer has already been marked, I don't have the reputation in this community to do so, but to address where your question stems from, with regards to how drones can be propelled forward, they often use propellers differently than your typical airplane. How they use their propellers, or how drones with propellers at the rear of the drone can still go forward, would be better imagined as being similar to how a helicopter can still move forward.
If you're referring to the rear propellers of a drone, I would assume you are referring to the rear propellers in a quadcopter setup. In simple terms, the drone is able to move forward by varying the speed of its front propellers from it's rear propellers. This is why when you see a drone move forward, you will see it begin to tilt forward as it begins to move forward, this is because the rear propellers are spinning faster and producing more thrust from its rear propellers, to create an intended imbalance of sorts, allowing it to lean and begin moving forward; simulating the same sort of forward motion suggested by the concept of "falling forward" when you run (though this terms should not be taken literally).
With a greater thrust pushing air "down" at the rear of the drone, the leaning forward of the drone helps direct the propulsion of the drone and redirects the force of moving air coming "up" (or the force pushing up on the rotor that is pushing air down) to be more at an angle (again, an oversimplification) which pushes the drone to move forward or whichever direction it is leaning towards.
While this is a simplified explanation, if you want a more physics-based answer that dives into the how the propellers work, the direction they spin, and explains things like angular momentum being the rotational equivalent of linear momentum, etc. you may want to check out this site. But, hopefully that helps you imagine or understand how drones can fly forwards, backwards, side to side, even with propellers in the rear.