A video game typically needs 3D models, animations, materials, icons, background music, sound effects, and maybe even voices and a cinematic clip for cut scenes. Unless you are Leonardo da Vinci, you won't produce all of this artwork yourself. Luckily, there are many game resource repositories where you can find game assets for download, and game developer communities with freelancing 3D artists.
You can either download free assets or buy pre-made multimedia collections. Each option has its pros and cons. Free models may not be available in the right formats. Commercial art packages may be expensive and in either case, you may not get precisely what you want. If you require maximum control over certain assets, your development team needs designated multimedia artists—and good multimedia software.