What type of hose for a pressure washer ?

WLM21

I've just been given a pressure washer, but I was not aware I'll need a hose too.

I have a normal garden hose, but it's a bit short to reach, for example my car.

Can I use an extendable hose with a pressure washer ...it's a karcher K2

TELLIT01

I don't see why not as long as you make sure it isn't kinking anywhere.  Personally I would get a conventional hose which is long enough.  They last far longer than extendible hoses and are repairable if they do leak.

Ectophile

I assume you mean the input side of the pressure washer.  If that's the case, any garden hose with a standard hose connector will fit a Karcher.

On the output side, you need special high pressure hose, or it may explode on you.