Coming a bit late into the party, this is one of those things one regrets not engaging in earlier on. The Game is not that easy to understand for those unfamiliar with collectible card games, but once you get the hang of it and the grasp of the potential value of collected cards over time, the wheels start turning.
Splinterlands game screenshot showing the currently most valuable cards within the game.
At first, I thought the cards were meant to be played physically, but somehow the game works out how one stack beats the other based on the speed, kind of attack/"weapon", extra abilities (both monsters and summoners), etc.
It is much simpler than that though, just follow the rules and choose cards based on total manna allowed as well as permitted elements, like fire, earth, or water... Once you click "Rumble", the game handles the rest.
https://splinterlands.com?p=battle&id=da43a092450e0344067534c395910c1a4aa39111&ref=techhype
It is interesting because it has also helped me understand the use of non-fungible tokens in a practical sense. Each monster is issued as either a common, rare, epic, or legendary card of a limited number. One can accumulate more cards as you mine more DEC or unlock them through the game reward system.
Eventually, if you feel you don't need a card or just want to trade it for Crypto or sell it for fiat, it can end up working as a worthwhile investment in the long run.
Apparently, it was easier for those who started early to win cards but as more and more players come into the game, they are going to be much harder to come by.