In Paladins, a 'Credit' is the form of currency that is earned in-match and does not carry over between matches. So spend them or lose them!
You can use Credits to purchase in-game cards that offer temporary boosts to a variety of categories (defense, attack, etc.). I personally turned on Auto-Purchase so that I didn't have to think about it (or risk forgetting about the feature altogether, since I'm not a hardcore Paladins player), and I end up auto-spending several thousand Credits every match with literally no effort on my part.
I mostly play Siege, so I'm not sure if other game modes offer more or less Credits, but either way you can still earn this achievement after a dozen hours or so of just playing the game and not even trying for it. Credits are earned via the following in-game methods (according to the game's wiki):
Standing near an objective:
- 4 Credits every 2 seconds while standing on the point in Siege and Onslaught.
- 6 Credits if there is an enemy contesting the point.
- 2 Credits every second while standing near the payload in Siege.
Capturing an objective:
- 300 Credits for capturing the point in Siege.
Killing an enemy:
- 30 + 10 * (Streak of killed enemy) Credits.
Eliminating an enemy:
- 15 + 5 * (Streak of eliminated enemy) Credits.
- 20 Credits for each 6000 damage dealt.
- 20 Credits for each 6000 hit points healed.
- Note that self-healing does not count (sorry Pip!)
- 20 Credits for each 6000 damage taken.
Absorbing damage with shields or deployable walls:
- 20 Credits for each 6000 damage absorbed.
Keep in mind that you gain additional credits for fulfilling your intended role in the game!
- Front Line champions gain 100% more Credits for standing near an objective.
- Support champions gain 100% more Credits for healing allies.
- Flank champions gain 30% more Credits for killing blows on enemies.
- Damage champions gain 100% more Credits for dealing damage to enemy champions.
I hope this helps! If you have any tips, please comment and I will happily add them in :)