At a basic level, GPU mining can be performed easily by running two commands:
geth --rpc
Once geth is up and running, and the blockchain is fully downloaded, Ethminer can be run in order to start mining. Ethminer is a standalone miner that can also be used in the farm mode to contribute to mining pools.
You can download it from GitHub here https://github.com/Genoil/cpp-ethereum/tree/117/releases.
$ ethminer -G
Running with the G switch assumes that the appropriate graphics card is installed and configured correctly. If no appropriate graphics cards are found, ethminer will return an error, as shown in the following screenshot:
Error in case no appropriate GPUs can be found
GPU mining requires an AMD or NVIDIA graphics card and ...
