It works best to have as many cards in a unit as possible, but there may be times when you find it nice to have slightly smaller units to be able to put more units out during a quest. Smaller cp units (units with a cp cost of 15 or less) do have a disadvantage to larger full units. Since it cost 5CP to just make a unit 20 1CP card can be put into 2 unit each totaling 15 for a total of 30CP or put into 1 unit totaling 25CP. 

Spell cards can also get ranks by adding more spell card to the unit. However, you may find that saving CP and GF also costs damage or Duration, so having 2 rank 1 spells may be better than having 1 rank 2 spell, and you still use up two spell cards to do both options. 

Finally as you level yourself and your units you will find that you will be able to field more units into each battle and be able to have more units in you army management screen. That is as long as the quest allows or PVP fights allows you to. 

You can also access the build option (quick key B in the game) and build new buildings such as houses and farms. (you will find that you will need farms right away and houses so don’t build much else until you can provide for you peasants needs. But you will soon be able to build up to get all you need. Also , be sure to build at least 2 or three store houses since you get a bonus for each storehouse. 

You will find that as you build you will run out of spots to build and you peasant population will still grow. Don’t worry there are quests to gain more territories and build more stuff. But be sure to leave space for a University since it will give you bonuses you will find you can’t live without. 

The market. In this building you can trade cards that you don’t want for cards you need. But be careful there are people out there that will try and take advantage of you. As a general rule, trade equal number of CP for the CP card you want. If you see a 6CP card try and trade a 6CP card for it. DO NOT SELL UNIT CARDS FOR RESOURCES unless they are common unit cards. Actually you can sell them for recourses but they are worth about 1000 per CP so if you are offered 1000 gold for a 15CP card reject the offer and try for better. But if you are running out of food you can ask for food. But try and get into a guild since they will help you out with some resources. 

Okay hopeful this should give you enough to start with. Like many games this one works best if you play around with it. Create a few nations, only one nation can be active at any one time and you can delete older nations if you find you like another faction better. But once you find out which one you want you will be tied to that one until you start buying packs. 

Common: These cards are available to be used by any faction in the game. You are able to get most of these cards from the in game Market, the exceptions being the cards that have 13 or more CP and all the spell cards. 

When you start a game you automatically start with 20 Human Archers, 20 Human Light Infantry, and 8 Human Light Cavalry, enough to put out two units in the tutorial quests. These cards have mostly passive abilities are good for augmenting you faction when facing specific threats, like Flying units, ranged units or machine type units.

Common Spells: