What does the verb "koskea" mean?

Shweta asks: 

Voisitko selittää verbi koskea englanniksi? Miten mä käytän?

My translation: 

Could you explain the verb koskea in English? How do I use it? 

Moi Shweta!

The verb koskea is quite a tricky one, as it has quite a lot of uses and meanings that all look quite different at a glance. According to Kielitoimiston sanakirja, koskea has five main meanings: 

1. to touch, as in to touch something with your hand:

Lapseni koski puhelimeeni likaisilla käsillään, ja nyt puhelinkin on ihan likainen!
My child touched my phone with dirty hands, and now the phone is dirty too! 

2. to get involved in something

En halua koskeakaan tähän asiaan! 
"I don't even want to get involved with this", so literally: I don't even want to touch this (topic/meeting/business..)

3. affect in a negative way

Työttömyys koskee monia ihmisiä. 
Unemployment affects many people.

Tämä asia ei koske minua mitenkään. 
This doens't affect me in any way.

4. to cause pain (literally or metaphorically): 

Vastaan koskee. = Vatsa on kipeä = Vatsaan sattuu.
(My) stomach hurts. 

Minuun koskee, kun luen Afganistanin kriisistä. 
Reading about the crisis in Afganistan hurts (me).

5. to concern: 

Nämä ohjeet eivät koske sinua.
These instructions don't concern you (or don't affect you). 

Tämä ohje koskee koko toimistoa. 
This instruction concerns (= is applied to) the whole office.

So the same verb can be translated to English in many, many different ways depending on the context it is used in.