Understanding your troops is the step you need to accomplish before fighting squads. You'll see soon enough how complicated this game can be and why, fully understanding what you have, will make your playing easier.
We will focus on squad fights. Fighting other players will be easier if you have a good army, despite not having Specialist so much developed.
You will start here. Trained in Barracks and cost Silver and Food. Controlled by captain's Leadership.
Guardsman
Human
Beast
Melee
Ranged
Mounted
Flying
Engineer corps are necessary to destroy walls. Trained in Barracks and cost Silver and Food. Controlled by captain's Leadership.
Engineer
Human
Siege
Monsters add to troops. Trained in Barracks and cost Silver and Dragon Coins. Controlled by captain's Authority.
Dragon
Elemental
Giant
Beast
Melee
Ranged
Mounted
Flying
From time to time you'll get Mercenaries. They stay with you for a period of 7 days and are controlled by captain's Dominance.
Complicated as it may seem, you will end up remembering those attributes pretty well. All troops mentioned above also share three attributes of great importance: Tier, Strength and Health. The bigger these three attributes, the fearsome your troops will be.
You'll start with Tier I and get to Tier II very easy. If you look at Guardsman attributes, you can see that Strength and Health are higher on higher tiers. You'll also see that, for the same type of guardsman, they eat the same and their revival cost is also the same. The goal is to get to higher tiers, so your troops are stronger and healthier.
The way to get higher tiers is to upgrade the corresponding technologies in the Academy. Before rushing into upgrades, see the Prepare strategy.
Since the food consumed and the revival cost are the same for the same kind of troops, it's unnecessary to keep lower tiers. In fact, it's a waste of resources.