After the cutscene, quickly get onto the nearest horse and ride towards the direction marked on the map. You need to reach Concord before time runs out.
Optional objective: Rescue civilian hostages.
In one of the villages you will receive an additional objective of saving the civilians.
Quickly turn left then, kill all the soldiers and move on towards the green points. As you reach the destination point, the second part of the mission will begin.
Optional objective: Kill groups of regulars with a single order - 7.
Optional objective: Completed all the constraints in one playthrough.
Now you will have to move trough three groups of shooters and give them orders with the interaction button. You need to do it when the approaching enemies will stop or stand close to each other. Don't wait for the order to be executed, instead immediately move to the next group. Whether a give group needs your help can be checked on the mini-map. Red dots will mark the attackers.
To get full synchronization, you need to approach the groups a bit earlier and press the interaction button when they are all already aiming at the British soldiers. They will then shoot more or less at the same time and therefore quickly eliminating the enemies. You need to do it seven times. Give further orders right after approaching a given group and afterwards move to other groups.
Your task is killing 130 enemies. Your progress is represented by the bar in the upper left corner of the screen. If losses amongst your forces will be too high, you will fail the mission.
After winning the battle, head to the marked spot and end the mission.