a preposition:
is a word or group of words used before a noun or pronoun to show direction, time, place, location, spatial relationships
for example
she often goes for a walk at night
i work on saturdays
i will collect data from february to june
a conjuction:
is a word that used to connect words, phrases, and clauses
for example:
they bought apples and oranges
it had been quiet since the children left