First thing to understand is, nothing is set in stone. I can say A, B and C and someone can point out a situation where this would be wrong. I could point out a situation. But for a beginner we need to take baby steps so to speak and keep it simple and basic. All of this is with regard to a traditional airplane with the motor up front and the propeller turning clockwise as viewed from the airplanes perspective. IOW as if you were sitting in the cabin looking forward out the windscreen.
A 5050 prop is 5 inches long with a 5 inch pitch. Typically such a prop will be labelled as a 5x5. The pitch number indicates the distance in inches the prop will travel with one complete rotation. That assumes everything is perfect and the prop is 100% efficient. They're not!
In your purchase you got both left and right handed props or Tractors and Pushers. Which, when in a package like that are typically for multi rotor drones as they use both. Typically fixed wing airplanes use tractor props and they're usually purchased individually. A few use pushers but the main clue to that is the prop/motor being on the tail end of the plane.
The prop loads the motor. The greater diameter and/or the pitch, the greater the load which, with electric, means more heat from both the motor and the ESC. You need to know what props, diameter AND pitch your motor will comfortably swing and stick with those sizes.
Also make sure your prop is on the right way. Flight performance can be negatively impacted by putting a prop on backwards. The prop blades should have one side that is curved like a wing and the other is flat. The curved is the front of the prop and should face the direction of travel and the flat is of course the back side of the prop and on a tractor configuration should face the airplane. A pusher would reverse this.
In theory you can replace a 5x5 with a 6x4. HOWEVER, with a 4 inch pitch the plane will fly more slowly. Maybe too slow to fly properly. Just one possibility you need to consider. Another possibility to consider is the shorter the prop, the less efficient it is. But like everything, there are limits. You can spend a lot of money on props if you allow them to hit the ground all the time.
The material the prop is made from is important too. Smaller inexpensive props are typically plastic. This plastic will vary in stiffness with some actually flattening out under power and thereby reducing effective pitch. The thinner plastic props can also deform from heat during shipment. Face it, they're cheap for a reason. A heavier plastic or carbon is a better choice for a small prop.
Regarding the battery, simply put voltage = rpm. The more volts the more rpm out of the motor and the faster/better the plane will fly. However, motors and ESCs are not designed to handle just any voltage you care to throw at them. You can have too much voltage/battery AND you can have too little. For now, stick with what the manufacturer calls for. As you learn, you will start to see what changes can be made, what effects they will have and how to do them safely and properly.
The angle you see on the motor is called offset thrust or right thrust. It's a method of improving some flight characteristics. You might see it point a little bit down too. If a model has it, keep it. If not, don't worry about it. I've never seen it make a significant difference except with serious aerobatic competition models. Not to say it can't help a sport model, I've just never seen it make that much difference. Just make sure it is always right and down if you have it. Never left and/or up. There are exceptions to that too but at this point you need to keep things simple.
FYI, a rule of thumb calls for all directions, i.e. left, right, up, down to be the airplanes left, right, up, down. So your left looking at the front of the plane is really the planes right.