STEAM NOOB Needs help

[Caveman]

PEr subject... I've been an ardent supporter of the IL-2 series and got many great years of enjoyment out of the sim.

I've been out of simming for about 4 years but I'm getting ready to come back in...

I want to pay a "good" price for COD despite the complaints it's not done, etc... I'm confident it will be the best WWII offering for years to come as the developers have already made great strides in a few short months...

All that said, I'm a noob at steam and have no idea how it works... My main concern is that if I buy the game now, can I keep the download code around forever to download it when I want instead of "now"?

I'm on the Ubisoft website (using a birthday coupon for $10 off) and it implies that software will be installed on the machine I download from etc...

Ideally, I just want to buy the right to download it now and then download it later on the machine of choice, etc... And what if I switch PCs? Then What?

Can anyone guide me along on what to do in this situation?