instantiating another script

I want to call another script from my currently running script. Actually, i want to call the Start and Update function as well , as the method i want to call depends on these methods. All initialization takes place in the Start method.

Is there a way to do it ?

What I would do is add the target script to an object and then disable it in the inspector with the little checkbox.

Then in the other script you can “enable” it at runtime. Therefore calling the Start() and Update() functions.