Important question, thank you for asking! Those are two of the major snake families; I know you only asked about two, but I'll discuss the big ones!
Pythons are a family of non-venomous constrictors. They're primitive snakes, meaning they have less stretchy skulls than modern families and they still have the vestigial remnants of a pelvic girdle. Pythons all have heat pits (except for the two members of the genus Aspidites) and those pits are set into the scales on their lips. Ball pythons, Burmese pythons, and rock pythons are all examples of snakes in the python family!
Boas are also non-venomous, primitive constrictors, and are closely related to pythons. They're distinguished, though, by having a couple fewer bones in their skulls and less teeth. When they have heat pits, they're between the scales instead of in them, and they're generally ovoviviparous and give live birth instead of laying eggs. Boa constrictors, anacondas, and rainbow boas are examples of this family!
Vipers are modern, venomous snakes. They have fewer bones in their skulls and less teeth than boas and pythons, and they lack vestigial pelvic girdles. Vipers tend to have primarily hemotoxic venom, and they're often heavy-bodied. When they have heat pits, they're located on their cheeks. Their fangs are hinged and swing out. Rattlesnakes, tree vipers, sand vipers, and copperheads are all members of the viper family!
Elapids are modern, venomous snakes who tend to have primarily neurotoxic venom. They tend to be diurnal and more slender than vipers, and lack heat pits. Their fangs are always set into position. Cobras, mambas, and sea snakes are members of the elapid family!
Colubrids are a large family of modern snakes. Most colubrids are non-venomous, and those who aren't are rear-fanged venomous, with a less sophisticated venom delivery system than elapids and vipers. They're a very diverse family of snakes! Hognose snakes, garter snakes, watersnakes, and ratsnakes are examples of colubrids!
There are other snake families, but those five are the really big ones. Understanding the differences means you also understand a lot of the commonalities and distinctions between common snakes!