This is honestly extremely simple.

void Kick(float kickStrength)
{
    RaycastHit hit;
    if(Physics.Raycast(Camera.main.transform.position, Camera.main.transform.forward, out hit)
    {
        if(hit.rigidbody != null)
        {
            hit.rigidbody.AddForceAtPosition(Camera.main.transform.forward * kickStrength, hit.point, ForceMode.Impulse);
        }
    }
}

When you want to kick something, do this:

Kick(100);

to kick with a power of 100, like so:

void Update()
{
    if(Input.GetKeyDown(KeyCode.Space))
    {
        Kick(100);
    }
}