calibers and numbers explained for dummies

Question
Can you please point me in the direction of an explanation from the very basics of calibers for rifles. I would like to learn all about the basics of centrefire, rimfire, .17, .22, Magnum, .223, .250, HMR etc. etc.
I am from Ireland and wuill be Fox Hunting.
I don't want to just buy a rifle and go. I want to know what is behind this technology a bit. Thanx

Answer
Hi
I would look over the Federal Ammo website.
It explains it fairly well.
http://www.federalcartridge.com/ballistics/default.aspx
Rimfire is primer is on the side id the rim.
These low power rounds.
Centerfire has the primer in the middle.
These are refered to as hi-power rifles.

Basically if your hunting at distances under 100 yards
go with .17 HMR or .22 Mag.
If your going longer ranges look at .22 Hornet .223 remington or .204 ruger.

You want to compare velosity bullet drop and energy.

You can find ballistic tables here as well
http://www.remington.com/
http://www.winchester.com/