すると

Two sentences can be joined by すると to express certain relations to one another:

1. The action in Sentence 1 causes what is said in Sentence 2
2. The action in Sentence 1 leads to the discovery of what's said in Sentence 2
3. From the info implied in Sentence 1, the speaker confirms that Sentence 2 is the case

It can be read as something like "then" or "thereupon", which makes sense in almost all of the instances I've seen it (since it's generally very common).

このアイコンをクリックして下さい。すると、コンピュータの画面の文字が大きくなります。
Please click on this icon. Then, the text on the computer screen will become larger.

メアリーは部屋に入ってすると、そこで小さいの男の子を見つけたんだ。
Upon entering the room, Mary found a small little boy there.

Ａ：田中さんは、明日の会議に出られないそうですよ。
Ｂ：すると、誰か他の人が出なくてはいけないということですね。
A: I hear that Tanaka-san can't attend tomorrow's meeting.
B: Then, that means someone else will have to attend.

リーさんはドアを開けてすると、子猫とねずみが遊んでいるのが見える。
Upon opening the door, Lee-san saw the kitten and the mouse playing.