Omar told www.themillers.co.uk: "I am very happy to be playing in English football and with Rotherham United.
"I have found the training very different from my time in Spain, it seems to be much more professional here. It has been hard but I'm enjoying every minute of it.
"Mark Robins has been very good to me, of course I'm new to this country and the lifestyle but the manager has been excellent in helping me settle into a new way of life."
Garcia is available for selection for Saturday's game against Rochdale and will be looking to make an immediate impression if he's drafted into the squad.