Since you want to be an artist in the game design industry, you can build your portfolio by creating 2D and 3D art creations.
Show how you create your creations from start to finish, and showcase your work on social media. You can gauge which style suits you more and which people like.
While you're creating your art creations, apply for internships. Like most jobs, having a an internship is valuable. It is your real-world experience that will help you in the long run.