By default, your military will be set to be aggressive which means that they will attack enemies on sight and will pursue them. However, there are many other options that allow you to customize their stance.
While setting your units to be aggressive may not seem a bad idea, it can be annoying in some situations, especially when your army continuously becomes scattered and disorganized after just spotting one enemy unit.
Units will pursue their targets, but only for a limited time before returning to their previous locations. This stance is good for patrolling units.
Military units will still attack but they will not move to attack unless ordered to do so. This is excellent for your army if you prefer them to remain organized, although you may need to order them to move, especially if they are under attack and they cannot counter the enemy.
Your units will never attack even if they are being assaulted by the enemy. This option is useful if your army is implementing an ambush behind enemy lines but this is not recommended to use if your units are being attacked.
Units will attack (and chase) civilians as their primary targets. This is helpful to prevent enemy civilians from constructing buildings, such as a redoubt.
Military units will destroy enemy buildings as a primary goal. This is helpful in destroying military producing buildings (such as the barracks).
By default, your civilians will be set to idle until they find something to do.
Build - This will set workers to build as a top priority.
Build and gather -
Pressing "shift" and right clicking on multiple locations/targets will order them to complete a "list" of objectives in that queue (see waypoints for more details).
Pressing "h" at any time when your selected units are moving will make them stop (and cancel any assigned waypoints).