South Korea took 12 shots and edged possession at Sun Life Stadium in Miami, but Ghana held firm and made the most of their opportunities on the counter-attack.
While Hong Myung-bo's side seemed to have Ghana on the back foot, they failed to hit the target throughout the friendly, while at the other end Jordan Ayew struck a hat-trick and captain Asamoah Gyan was also on target.
The win ended Ghana's two-game losing streak in the lead-up to the FIFA World Cup, after 1-0 defeats to Montenegro and the Netherlands.
''You learn from your mistakes," Appiah said in his post-match press conference.
''Korea attacked really well. Playing against players with good pace, you have to be cautious in the back. We made good use of the counter-attack chances we got.
"The scoreline didn't matter to me. I am not looking at the scoreline, I am looking at how best I will prepare my team."
Appiah claimed he had no information on an injury to Abdul Majeed Waris, after the Valenciennes striker was forced off in just the sixth minute following a sliding challenge from South Korea's Ki Sung-yueng.
"The doctors are still working on him. I mean I'm hoping to get the results of the extent of the injury in two (to) three hours time," added the Ghana boss.
"At the moment, I haven't had any information yet. I hope he recovers to join the team."
Waris was replaced by Ayew, who went on to strike his maiden international hat-trick.
Ghana open their World Cup campaign with a game against the United States on June 16.
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