To build up your attack and defense strength, you must recruit soldiers and equip them with weapons. You may also hire mercenaries or train your soldiers. To recruit soldiers you must have people click on your unique link (you can find this in your Command Center). Each time you recruit an additional soldier, your attack and defense strength will increase slightly, as will the amount of gold you receive per turn. Also, for every two recruits each of your officers gets, you will receive an additional soldier! The number of officers you can have is unlimited, so the more people who sign up to be your officer the faster you can build your army.
In addition to those soldiers generated by unique link clicks, you can choose to conscript soldiers - once a day you will recruit a number of soldiers determined by your current 'unit production' value. This value can be upgraded on the Training page.
To train your soldiers, use the Training page. Soldiers can be trained to be specialists in either attack or defense - whichever you choose, they will boost that ranking further, while ceasing to contribute to the other ranking. You can also train soldiers to become spies or sentries, which will be discussed in more detail later. In this case they cease to contribute to your attack/defense strength and the amount of gold you get per turn, as instead they are being kept in readiness for any covert missions you may choose to send them on.