Metal Gear Solid 2: Sons of Liberty/Getting Started
Metal Gear solid 2 is a stealth game. Avoiding combat is the best option. The enemies have stronger weapons, and there are infinite amount of them, and only one of you.
 Sneaking Mode
When the enemy isn't alert of your presence or if they are not searching for you, you are in sneaking mode, or normal mode. This is what you will start the game with. In this mode, guards are patrolling certain areas and some guards may be alerting their commander of what they find via radio. If a guard hears a noise, they'll come over to where the sound was and investigate. If nothing is there, they resume their patrol. If you enter their blue field of vision or if they find you, they will try to call for backup. If you knock them out in time, they won't succeed. Warning: The commander will send guards to investigate what happened.
If the guard does call in backup, the game goes to alert mode.
 Alert Mode
When the entire enemy base acknowledges your presence. The enemy will try to kill you. You must hide to escape this mode.
When you escape the enemy and they try to search an area.
When the enemy fails to find you, they will be on full alert. If this ends, the game goes back to Sneaking mode.