Where can we read about what exactly is Ropsten and it's influence to the Etherium in general?
The Ropsten test net is essentially used as a testing environment before you bring your code onto the main net. In contrast to the main net, writing to the test net is free. I think there may be some other differences to the ropsten test net vs. main net, but I'm not certain as I haven't read the specification and I'm not really sure where it's at.
The Ropsten test net is also likely to be subject to change in the future, as it has been in the past. Before there was a test net called Morden. It was retired due to replay attacks (read more here: https://blog.ethereum.org/2016/11/20/from-morden-to-ropsten/) There are discussions now about using a test net that utilizes something called Proof of Authority and there is currently one live dubbed, 'Kovan'
So highlights of ethereum test nets.
Deploy untrusted code to the test net rather than the mainnet.
It's pretty much free to use (unlike the main net).
It's subject to change.