There is no magic QMultiplayerOnlineGameServer or Client class if that is what you are expecting. The task in front of you looks like this (order may vary):
  • Design game logic
  • Design communication protocols
  • Design client
  • Design server
  • Build client using Qt or other libraries as appropriate
  • Build server using Qt or other libraries as appropriate
  • Host server somewhere
  • Distribute client
  • Profit?