function vs software program

function and software program both are nouns.

Word	Noun	Adjective	Verb	Adverb
function	Yes	No	Yes	No
software program	Yes	No	No	No

As nouns, software program is a hypernym of function; that is, software program is a word with a broader meaning than function:

function: a set sequence of steps, part of larger computer program
software program: (computer science) written programs or procedures or rules and associated documentation pertaining to the operation of a computer system and that are stored in read/write memory

Other hypernyms of function include computer software, package, software, software package, software system.

function (noun)	software program (noun)
the actions and activities assigned to or required or expected of a person or group	(computer science) written programs or procedures or rules and associated documentation pertaining to the operation of a computer system and that are stored in read/write memory
what something is used for
a set sequence of steps, part of larger computer program
a formal or official social gathering or ceremony of people
a formal or official social gathering or ceremony
(mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)
a relation such that one thing is dependent on another

function (verb)	software program (verb)
perform duties attached to a particular office or place or function
perform as expected when applied
serve a purpose, role, or function