Stealth

An enemy is always in one of two states: aware of your presence or unaware of your presence.

If they are unaware, you make a Smarts +d20 vs. Senses + 10 check every round to remain hidden from them. You have to have some sort of concealment to make this check, otherwise they will spot you on the second check if they didn't on the first. Concealment can be darkness or cover. Your DM will decide what the bonus you get from them is. If it is the night or late night block, you get a +3 bonus to stealth checks.

If they are aware, you must exit their field of vision, whether through moving around a corner or otherwise blocking their view of you. You can then make a Stealth check to become hidden, as above, but with a -5 penalty.

If you fail a Stealth check, nothing changes in the battle. Everyone knows where everyone is. If you succeed, your enemy does not know you are there, and as such you are Hidden from them. You must make a separate check for every enemy present if you wish to hide from multiple enemies. If you fail one, you fail all of them.

Once you are Hidden from an enemy, you get a +5 bonus to your first hit roll against them.