first person controller help

I am using a first person controller to move my character in a game but my first person controller and character keep falling through the terrain I have colliders set up and nothing is marked as a trigger so what is happening that needs fixed?

Use a rigidbody and a capsule collider, freeze the objects rotations though. Then you can use the velocity change forcemode to achieve the velocity you want. Sorts out all collisions nicely and even allows characters to push one another around if you want that.

public Vector3 targetVelocity = Vector3.zero;
	
void Update(){
		Vector3 vel = targetVelocity;
		vel -= rigidbody.velocity;
		vel.y = 0;      //prevents person flying
		rigidbody.AddForce(vel, ForceMode.VelocityChange);
	}