Ethereum is an open-source, public, blockchain-based distributed computing platform and operating system featuring smart contract (scripting) functionality, which Ether is a cryptocurrency whose blockchain is generated by the Ethereum platform. 

Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed. Ethereum provides a decentralized Turing-complete virtual machine, the Ethereum Virtual Machine (EVM), which can execute scripts using an international network of public nodes. 

ETH "Gas", is an internal transaction pricing mechanism used to mitigate spam and allocate resources on the network, as well as a reward method for miners for being executing the transactions. The transaction after is requested, go to a pool with other transactions, in which miners will pick the ones with higher gas first, to after put them in blocks to add to the chain. They can also choose to include no transactions in the blocks, or they can choose to randomly select transactions. 

In either way, setting up a gas price too high can also not be a good idea and if the limit is set too low, then the transaction is at a risk to not be accepted by the network either. 

You'll pay the computation regardless of whether your transaction succeeds or fails. To know about the gas, please check Ether Gas Station.

At CoinField, we offer ETH with a pairing on XRP, as well to other Fiat currencies, such as CAD, USD, EUR - for buy and sell.