Clear and precise communication is important when you're flying, because always, safety is foremost. Therefore, when pilots are talking to air traffic controllers, the need for clarity is vital. Also, when you are another aircraft monitoring radio transmissions of pilots flying around you, any message that isn't understood correctly can have critical consequences. Therefore, civilian and military pilots (as well as U.S. ground military forces) rely on the phonetic alphabet to clarify communications and prevent misunderstandings.
If you plan to fly as a pilot, learn the phoenetic alphabet now. Here it is:
A: Alpha, B: Bravo, C: Charlie, D: Delta, E: Echo, F: Foxtrot, G: Golf, H: Hotel, I: India, J: Juliet, K: Kilo, L: Lima, M: Mike, N: November, O: Oscar, P: Papa, Q: Quebec, R: Romeo, S: Sierra, T: Tango, U: Uniform, V: Victor, W: Whiskey, X: X-Ray, Y: Yankee, Z: Zulu.