How do you avoid confusion when spelling things out verbally, particularly when the sound isn't clear or there may be background noise? So, for example, something like Y I V B D T doesn't unintentionally get heard as Y Y B P D D. Or perhaps as I Y P V T D. A lot of letters sound similar.
A phonetic alphabet, or spelling alphabet, is a way to ensure all letters are unambiguously heard correctly by using words starting with each letter. The set of words was chosen from 1,000s of tests, including real-life ones, to maximise clarity and avoid overlapping sounds with other letters that might cause mix-ups. When written out they include deliberate misspellings Alfa and Juliett to avoid misinterpretation.
The NATO phonetic alphabet is a standard one, but there are other variations.