A Charge Attack is a Full-Round Action a character can perform which allows them to move faster and farther than normal and attack a target at the end of their charge. Even better, performing a Charge Attack doesn't provoke Attacks of Opportunity, and charging gives a character a +2 bonus on Bull Rush Combat Maneuver checks.
A charging character moves up to double their normal movement speed, and must move at least ten feet. They must also have an unobstructed route to their target - they cannot charge through one enemy to reach another. When the charging character reaches their target, they'll get to perform a standard melee attack with a +2 Attack Bonus. Charge Attacks are somewhat reckless, however, and the charging character will suffer a -2 Armor Class penalty until their next turn.
You'll find the Charge Attack ability in the Abilities tab (the middle tab) above the action bar.