If you were one of the lucky few to gain access to the Legends of Runeterra card game during the beta, you might have unlocked a form of currency known as Shards.
Shards, unlike Wildcards that can be bought with actual money, are essentially the free currency in the game. You can use Shards to buy one of any card so long as you have enough, so grinding and farming a lot of them is the best way to play the game completely for free.
Unfortunately, there isn’t any specific way to earn them at least in the preview phase of the game, as they are unlocked as rewards during the Prologue or Region Rewards section of the game.
You could, in theory, just keep playing games, grinding away at EXP till you collect some of the early shard rewards from each Region, but it’ll still take some time.
We imagine eventually players will earn a few shards from daily rewards and through playing the game similar to how League of Legends works. But considering the game is still in its early stages, anything could happen.