Go through some of the in-engine tutorials. Blueprints, material editor, and sequencer to start. The cards could be created as two-sided plane meshes, or ultra-thin cube-based meshes. What I mean by cube-based is start with a cube, resize it to be say…6 x 4 x 0.1 (where 6 is height or Y axis scale, 4 is width or X axis scale, and 0.1 is thickness or Z axis scale). Then create materials for the card appearance (like the border, an empty space for a picture / illustration / animation, certain areas for text to write stats / description / abilities / etc). It wouldn’t only involve materials, but probably also creating a UI template(s) for various cards and their types. That is one of the most important things to research how to do correctly and efficiently.
For the playing field, there needs to be materials / textures to apply (such as a wood surface for a table or something). Do the in-engine tutorial for Cascade and/or Niagara (it’s a plugin that may need to be enabled under Engine > Plugins). Do a search for how to create a CCG or strategy card game on YouTube or other video sites, in Unreal Engine 4. Look for artists interested in doing art for that kind of game.