Using copyrighted material without proper authorization can lead to copyright strikes, demonetization, or even the removal of your videos.  YouTube's Content ID system automatically detects copyrighted content, and copyright holders can take action against unauthorized use.  To avoid issues, use royalty-free music, create your visuals, or obtain proper licenses for any copyrighted material you want to include.  Prioritize creating original and unique content to build a sustainable channel without legal troubles.