Advice controling speed of a rigidbody

Trying to understand how to best use rigidbody to set or changing an objects speed.

I see AddForce but appears takes a vector3.

I have defined a speed (float) for my object.

It appears if I want the velocity (vector3) of an object I should do AddForce (vector3).

This appears to mean I must convert my objects speed into a vector based on the objects orientation and then set AddForce.

Is this the way to do it? Ther must be an easier way where I can set the speed (float) I want and let Unity figure out the addforce vector?

I think I found my answer.

transform.forward is essentially the unit vector of the direction/orientation of the GameObject, correct?