So, is there a need to know the difference between Ethereum and Ethereum Classic?
The ecosystem of this brand of currency works via a smart contracts approach. These are all automated. When the brand was being established, it relied on the so-called DAO - Decentralized Autonomous Organization.
Some history here: To get a say in DAO, one would need to buy special tokens sold only in exchange for Ether. Closely connected to control of the process were the curators. The system also involved a vote of approval for all major decisions regarding the whole currency system to be passed. This was a virtual way of building the checks-and-balances system of the organization. And it failed.
Tip: Before there was ETH and ETC, there was only one currency, and then, a solid sum of money was stolen from the Ethereum fund due to the loophole in the DAO system. Since then, it has been a battle of ideologies and ethics between ETH and ETC.
The scandal with the money theft proved DAO to be insecure, but it did not mean the currency was. And it still does not mean that.
While there are till this day ideologic (and some software) differences between the two currencies, when it comes to using ETC, the bottomline is your money is safe. Ethereum uses a blockchain absolutely different from that of a Classic version. Both still support a peer-to-peer algorithm, cash exchange (yes, Ethereum Classic can be converted back to USD), and a classic wallet system.
In order to pay online with the reviewed currency, you will need to register an account and to get yourself some ETC. This is possible by either buying Ethereum Classic or by getting it from peers. This is still a volatile currency, so Ethereum Classic price will change from time to time.