Re: What do I do with Cards - Not gaining XP

@canoso99 
If you're playing the Campaign, Arcade mode, or Instant Action mode you won't gain any XP.

Only Online modes grant XP

Anything under the Multiplayer Tile on the Play Tab, plus Co-Op mode. This includes: Co-Op, Galactic Assault, Supremacy, Heroes Vs Villains, Hero Showdown, Blast, Strike/Extraction, Starfighter Assault, and Hero Starfighters. The only Multiplayer exception is Ewok Hunt

Also there's a recent BUG that's making you not gain XP with the Heavy Class in the Supremacy mode, on the map Scarif only. But as a new player I think you can ignore this line.