Documentation not explain how to utilize GPU

I am very new in ZCash and want to mine under linux.
zcash after run said:
"To enable mining, add 'gen=1' to your zcash.conf and restart."
Also here is explained how to enable CPU mining,
but what about usual GPU mining? Is it on , how to turn on GPU mining?

Thank you!

You need a suitable miner. Use Claymore or Optiminer for AMD cards or EWBF for NVIDIA cards