Select Mortal Kombat from the main menu and fight your way up the ladder until you've defeated all kombatants. Shang Tsung is the final boss.
One of the easiest ways to win is to keep jumping back and kicking in the air. Even against the wall, continue to jump back and kick. The computer will walk into your foot every time.
Goro: He's a big, four-armed pain in the ass but is fairly simple if you pick Sub-Zero and keep freezing Goro in place ( ) just as he gets up from a knock down. Uppercut while frozen for maximum damage.
Shang Tsung: You'll want to duck under his 5 fireballs as they take off half your health. Go Liu Kang and when Shang is more than half screen away from you, do his flying kick then jump back and try to repeat. Timing is important and watch who he morphs into. They will use their special moves to the fullest so learn to avoid and try to only attack when Shang is on screen!