The Rally Spot is a place for military assembly, where you can give an order to attack or conduct a military exercise, check your army's status and intelligence, adjust your attacking and defending strategy. The level of the Rally Spot determines both how many marches you can send out at any given time and the maximum size these marches can be. Per level, you can send one additional march and the march sizes increase by 10k troops, all the way up to level 10 which can send up to 10 marches, each consisting of 100k troops. Also note that using a War Ensign item can increase the size of a specific march by 25%.
The 'Open Gate to Fight' option determines whether your army adds its strength to the city defenses, or stays safely in barracks to leave the wall defenses to take on an attack unaided. Leaving your gates closed is useful when you think your army will die from an oncoming invasion and want to protect them. Another feature of opening gates is that your scouts will combat enemy scouts when they come to scout your town and potentially kill them before giving the enemy any information; having your gates closed prevents this and lets enemies scout you freely.
March: Instead of going to your selected target on the map and choosing to send a march, you can send it directly from your Rally Spot if you know the co-ordinates of your destination.
Exercise: Exercise is a troop vs. troop battle simulator that will give a rough idea of what might happen in a battle between specific army combinations. This is handy if you're unsure what formation to put your army in, or wondering how to reduce your losses, but it has some flaws. It doesn't include technology levels, traps and wall durability or Hero attack statistics, all of which can majorly swing the outcome of a battle. Because of this, it's advised to not use the Excerice unless you know the enemies information and can accurately put it together in accordance with your own to come to a better conclusion about what might happen, but is still gives innacurate numbers at best.
Medic Camp: In the rally spot you will find a button that says medic camp. This holds all of the troops that have been wounded in your recent battles. For a gold fee you can 'heal' these troops and they will rejoin your army. If you don't heal them they will eventually die.