All snakes in all the world are members of the order Squamata. This order also includes the lizards. This shows that snakes and lizards are very closely related. Snakes belong in the suborder Serpentes -- the serpents. -- while lizards belong in the suborder Sauria.
The main differences between lizards and snakes are:
There are about 2,700 snake species in 11 snake families worldwide, of which about 115 species in five families -- depending on your expert -- are found in North America north of the Mexican border. Below is a list of North America's five snake families:
Colubrid Snake Family -- the Colubridae (many kinds of snakes in this largest of all snake families, found nearly throughout North America
Here are the main groups of Colubrid snake:
Coral Snake Family (venomous) -- the Elapidae (In the US, only in the Deep South & southern Arizona & New Mexico)
Pit Viper Family (venomous) -- the Viperidae (in most of the US)
Slender Blind Snake Family -- the Leptotyphlopidae (really slender & blind, in North America found only in the US Southwest; seldom seen)
Boa & Python Family -- the Boidae (large, thick snakes, in North America found only in the western states and southern British Columbia)
From the above we can see that nearly all the snakes we can expect to find in our immediate neighborhoods, assuming we're not near a natural or semi-natural area, will belong to the Colubrid Snake Family.