Combat is the core of the kaiju experience - so having a strong combat plan is essential for victory. There are many aspects you can tune your combat deck around:
At the top left of the card we have a cost expressed as some number of red/blue/yellow boxes, which represent Ferocity/Agility/Power respectively. Finishing Blow, for example, costs 3 Ferocity to play. Over the course of a fight you might want to play 5 or more combat cards, so it is very easy to run out of Ferocity, Agility, or both!
These icons are only used when constructing your deck - a valid combat deck MUST have an identical number of sword icon cards and shield icon cards. Finishing Blow is a Sword-icon card.
Finishing Blow has two keywords : skilled and punch. Many character abilities or combat card texts focus on keywords, usually it terms of damage bonuses. Finishing Blow is a CHAIN type card - so it has a green top-bar color. Specifically, it is a Chain Attack. Some card or character abilities refer to card type - especially DODGE cards, which are unaffected by either CHAIN, QUICK, or FIERCE cards.
All cards list either Damage or Toughness. (Technique cards list both!) Along with some icons. Each icon represents a +1 bonus if the character playing that card has the appropriate trait (Claws, Horns, Tail, Teeth, Wings, Spikes, Armor, or Shield.) Icons in RED indicate a PENALTY of -1, if your OPPONENT has the appropriate trait. (most weapons, for example, deal less damage to opponents with the SHIELD trait.)
Finally, most combat cards (but not all!) have text which details specific rules for that card.
Energy Tokens allow characters to play cards which are too expensive - though Energy Tokens are very limited, so they should not be used carelessly. Each Energy Token spent replaces 1 Ferocity or Agility you cannot otherwise pay. Yellow boxes represent costs which MUST be paid with Energy Tokens.
When looking at your hand of combat cards, it is a good idea to first identify whether or not you can play ALL of the cards in your hand. If you cannot, you should immediately prioritize which cards you can and cannot play with your given character. (If you usually cannot afford your entire hand of cards - you might want to consider adjusting your Combat Deck to cost less!)