Answer:
Accents arise through different pronunciation of vowels and consonants, stress, and rhythm, stress and intonation.
Often this happens because of geographical barriers so an accent may identify the locality in which its speakers reside (a geographical or regional accent).
As human beings spread out into isolated communities, stresses and peculiarities developed. Over time these developed into identifiable accents.
Also an accent may identify the socio-economic status of its speakers, their ethnicity, their caste or social class, their first language (when the language in which the accent is heard is not their native language), and so on.