When you create a new splinterlands account which costs 10$, they give you 3000 credits to start with so you can buy or rent some cards on the market.
1000 credits = 1$ and you can only use those credits to either buy or rent cards in splinterlands.
So, i spent 125 credits or about $0.125 worth on rentals and was able to come with a small profit after 24h.
Here you can read my follow up:
@archmagebot/archmage-bot-running-on-brand-new-account-day-1