Combat is divided into 20 second rounds. An attack roll does not necessarily represent a single attack, but rather the cumulative result of a full round of fighting.
Initiative 1d6+ Dex modifier.
Move action: Move a number of inches equal to your speed, switch weapons, or make additional range attacks
Attack Action: 1d20+Attack Bonuses+Targets AC. 20 or greater hits. Damage is by weapon, modified by your ability modifier.
For every 3 points higher your Base Attack Bonus is than your enemy’s, you gain a free attack that does not receive your BAB.
Ranged weapons are attacking within their range increment are at +2 to hit. Beyond that but within double their range increment, they are at +1 to hit. Their maximum range is triple the range increment. If you do not use your movement action, you can take a number of shots up to the weapon’s rate of fire. If you fire more than one shot, you do not receive your dex bonus to damage.
Enemies that prone, entangled, unaware, similarly disadvantaged are at a +2 to hit.
Unarmed strike: 1d2 + STR mod.
Grappling: Each side rolls 1d6 for every level they have. Higher side wins, defender’s advantage.
Save or Die/Suck has largely been replaced with Ability Score damage. Poison deals STR damage. Petrification and Paralyzation deal DEX damage. Successful Saving Throws will halve the damage dealt. Death effects deal CON damage. And so on. Death/Petrification/Paralyzation etc. occurs when the affected stat reaches 0. Healing this damage will depend on the effect causing it.
HP heals at a rate of 1 per day, two if it is a day of rest.