Once you understand the reason for this armed conflict, then you can move forward. Interspersed throughout this war will be your iconic scenes, the battle and the siege. One thing to remember: Open battles are not nearly as common as believed. The siege, on the other hand, is.
The reason? Battles are extremely costly, and going into one, each side must agree on that cost, which is the lives of their men. One side, regardless if it is a draw, will lose. Confusing? Yes. Both armies may fall back and decide that another charge would be pointless, but the damage is done regardless. Hundreds, if not thousands, will be dead, and many more will be injured. The side that can accept these losses will actually win the draw.
What occurs more often is the siege. One force, knowing it is outnumbered and outgunned, will fall back to a stronghold and prepare for siege, where it’s disadvantage of numbers is reduced. The more powerful army will then roll up and prepare to besiege the stronghold. Again, the assault is also rare. Many armies will gladly pick away at the defenders, trying to force them to submit by starvation or disease. Assault is used when haste is needed or an exploitable weakness is found. Perhaps winter will soon be upon you, so either you assault and take the town at the cost of lives, or withdraw and wait for a more opportune time that may never come.