Often there are many natural and man-made obstacles and terrain features on a battlefield that can be used to gain an edge over an opponent. Cover is using features to increase your defensive capabilities while elevation increases your offensive capabilities

Cover Bonuses

Type
Melee (physical damage)
Ranged (physical damage)
Shrubs, Hedge, Fence
none
+5 AC
Trees, Wagons, Barrels
+5 AC
+10 AC
Boulders, Walls
+10 AC
+15 AC
GM discretion in specific situations over rules

Elevation Bonuses

Slightly Elevated, up to 3 feet (i.e table): +2 to hit with melee and ranged
6 feet above: +4 to hit with melee (if applicable) and ranged
12 feet above: +6 to hit with ranged only
18 feet above: +8 to hit with ranged only
18+ feet above: +10 to hit with ranged only