Well its not too hard, basically computers like mine shore up the network and provide the "infrastucture" to run things on what is called the block chain. I am rewarded for this work by a percentage of Ethereum and run the miner on a group so we collectively mine (called a pool)
Payouts are sent to a wallet, graphics card prices have gone through the roof due to this, at current prices a 2k rig will make you around £450 a month (thats after paying electric etc and fees) so pay off your equipment and you could have a few quid a month for the sake of a pc running in the background.
However the market is very volatile and it could all crash and be worthless, hence why using graphics cards is useful as they will have residual value to sell to gamers angry at us for using all their cards to mine crypto currencies.
The whole crypto currency thing is quiet complicated and can often get mixed up with anonymity and bad stuff, however transactions are all recorded and the whole concept of the currencies was to take the power out of greedy banks using your money to do whatever the fook they like. Hence why they now moan and say this is dangerous and not something to invest in lol