What is Bitcoin mining?

So I've been researching Bitcoins and trying to get a full understanding of how they work. But what I can't understand Is what the term 'bitcoin mining' means. There's some information online but I really can't make much sense of it! I'd really appreciate it if someone could explain what it is, how it works etc! Thanks

 

Mining is where you help process transactions in the block chain and also you can mine new blocks which are worth 25 bit coin each, usually you mine within a pool.

You need a ASIC mining system now, GPU mining is dead for Bitcoin.

 

What is this ASIC mining system, what does it actually do, i understand it mines bitcoins, but what is mining bitcoins? I read somewhere it was something to do with cracking codes or something? I'm really lost Also, is it actually worth doing?

 

google avalon or butterflylabs they sell ASIC units.

 

It's what ESEA did to scam resources of thousands of subscribers to use rthier machines to make Craig Torbull even more money.
http://www.theverge.com/2013/5/2/4292672/esea-gaming-network-bitcoin-botnet