One of the prepositions that takes the genitive case is из, which means ‘from’. But not all froms are created equal in Russia. Let's start thinking about to/from/at in Russian like this. There are three words for to, three words for at, and three words for from. And they are related, roughly speaking, like this:
|If you go "to" a place using…||then you'll be "at" that place using…||and you'll return "from" that place using…|
|в + acc||в + pre||из + gen|
|на + acc||на + pre||с + gen|
|к + dat||у + gen||от + gen|
So if you go to a place using в, and you are at that placе using в, then you come back from it using из. That applies to most cities and countries and places of business:
|Она только что пришла из аптеки.||She just came back from the pharmacy.|
|Он только что приехал из Москвы.||He just returned from Moscow.|
|Мы только что прилетели из Гонолулу.||We have just returned [by air] from Honolulu.|
|— Откуда он?
— Из Перми.
|“Where is he from?”
These aren't the only contexts which require из, but it's a good start to keep them in mind.