The Charge sub-phase is perhaps the most important part of the Movement phase – this is where you'll unleash your forces to the bloody work of close combat. Battles can be won or lost on the timing of a charge. Charge too soon, and your troops will tire and lose momentum before they reach the enemy and the charge will fall short; wait too long and the enemy will instead charge you; but choose the right moment and the momentum of the charge will sweep your warriors to glorious victory.
In this sub-phase, you'll choose one of your units and declare the charge you want it to make. Your opponent will then have the chance to have their unit hold its ground or react to the charge, either by standing and shooting or fleeing.
Once the charge reaction has been resolved, you can nominate another of your units to declare a charge, and so on, until all of your charges have been declared and reacted to – then you get to make your charge rolls and resolve the charges.