The influences upon punk music are obvious: Garage rock (mostly US, from the late sixties), Eddie Cochran, Kinks, Troggs, T-Rex, so-called pub rock from the UK (e.g. Eddie And The Hot Rods), MC5, New York Dolls and also Can, Beefheart and Bowie. The punk bands were respectively influenced by different bands or musical epochs: The Clash by late fifties and sixties; The Damned by the seventies; Buzzcocks and Siouxsie And The Banshees had clearly heard a lot of Can.
There was never a uniform style of music: Ramones, Buzzcocks, Banshees, X-Ray Spex, Clash, Sex Pistols, Damned, Sham 69 all sounded different to each other. Uniformity of style didn't appear until the eighties when a "punk sound" was declared, a style that has existed until today. (Today, a "punk" band blandly sounds like a cross between Ramones and The Clash.) Musical similarities existed of course: Tempo, absence of seventies-style guitar solos, brevity of most songs and a traditional verse-chorus-verse song structure.
An important common factor of punk bands was that there were no restrictions at all on what was required to be the lead singer: John Lydon, Mark Perry, Pete Shelley, Siouxsie Sioux, Poly Styrene, Joey Ramone, Jimmy Pursey, Joe Strummer, Dave Vanian – and also Paul Weller – were never singers in any formal sense nor as how rock music lead singers were supposed to sound. This is a key point. All the lead singers named above have distinctive voices that were a vital part of the respective band's popularity and longetivity, and some have had a huge influence on singing styles since, most notably Sioux, Styrene, Lydon, Perry and Shelley.
Equally important, and the reason why the music remains popular today, is the fact that there were great songs. 'New Rose' is one of the finest pop songs ever, 'Germ-Free Adolescents' is packed full of wonderful tunes and Pete Shelley had four years of prolific classic songwriting ('Ever Fallen In Love', 'Promises', 'What Do I Get', 'You Say You Don't Love me', etc. etc. etc. ) that, in terms of quantity of quality, has only been bettered by Bowie and The Beatles. Punk would have been nothing without the tunes.
Musically, punk lasted barely two years. The more popular bands disappeared (X-Ray Spex, Sex Pistols), developed musically (Siouxsie And The Banshees, The Clash, Buzzcocks) or became caricatures of themselves (Damned, Ramones).