すると, a combination of する and the
conjunction particle と, is generally considered to be an abbreviation of
そうすると, and means that 'once (A) is done, (B)', or 'upon (A), (B)'.
すると is usually used at the beginning of a new sentence, to highlight something that occurred due to the circumstances mentioned in the previous sentence/statement.
As a standalone statement,
すると is classified as a
conjunction.
久（ひさ）しぶりに押入（おしい）れの掃除（そうじ）をした。すると、無（な）くしたと思（おも）っていた服（ふく）が出（で）てきた。
I cleaned my closet for the first time in a long time. Upon that, I found clothes that I thought I had lost.
お祖母（ばああ）ちゃんが川（かわ）で洗濯（せんたく）をしていた。すると、川（かわ）の向（む）こうから桃（もも）が流（なが）れてきた。
An old lady was washing her clothes in the river. Just then, a peach flowed down the river from a distance.
The 'result' that
すると conveys, should always be one of two specific things. Something that the speaker has no control over, or a conclusion/determination that the speaker wants to confirm is correct (based on their understanding of the previous statement).
猿（さる）にバナナをあげた。すると、猿（さる）がどんどん集（あつ）まってきた。
I gave a banana to a monkey. Having done that, more and more monkeys started to gather around me.
19歳（さい）なの？すると、大学（だいがく）1年生（ねんせい）でしょう？
You are 19? So you mean to say that you are a freshman, right?
When
すると is used to draw a conclusion about another person's statement, the translation is closer to 'so you mean to say (A)', or 'if so, then (A)'.