To add collision to an FBX 3D model, import it into a 3D engine (e.g., Unity, Unreal) or tool and generate simple collision shapes (box, sphere, convex hull) that match its geometry.
Collision shapes act as the model’s "physical boundary" for interactions like collisions—using simpler shapes instead of the original detailed mesh keeps performance smooth.
In Unity, select the imported FBX, go to "Add Component" > "Collider," and pick a shape: Boxes/spheres work for basic models, convex hulls for irregular ones.
If you’re new, start with basic shapes (box/sphere) in Unity—they’re easy to set up and test before trying convex hulls for complex objects.