A Generalization (hallmark differences):
Boas and Pythons are subfamilies of Boidae.
Colubrids: A large grouping of snakes that aren't boas, pythons, vipers, elapids, hydrophiids, leptotyphlopids, etc, etc. Colubrids are generally oviparous but there are exceptions.
There are many more differences and some animals will overlap and add to the confusion, taxonomy is rarely cut-and-dry.