selection vs assortment

selection and assortment both are nouns.

Word	Noun	Adjective	Verb	Adverb
selection	Yes	No	No	No
assortment	Yes	No	No	No

As nouns, assortment is a hypernym of selection; that is, assortment is a word with a broader meaning than selection:

Other hypernyms of selection include miscellanea, miscellany, mixed bag, mixture, motley, potpourri, salmagundi, smorgasbord, variety.

selection (noun)	assortment (noun)
the act of choosing or selecting	the act of distributing things into classes or categories of the same type
the person or thing chosen or selected	a collection containing a variety of sorts of things
a passage selected from a larger work
an assortment of things from which a choice can be made
a natural process resulting in the evolution of organisms best adapted to the environment