Creating custom unit module

You need is to create a new C# Script, and place your logic here. Inherit it from BaseUnitModule (or UnitLogicModule, if you need a per-frame Update) — these are the base classes for all unit modules in RTS Kit (plain C# classes, not MonoBehaviours). They contain a link to the main Unit component, so you can easily access it from your own module, for example:

using UnityEngine;
using InsaneSystems.RTSKit.Gameplay;

public class CustomModule : BaseUnitModule
{
  public override void Start()
  {
    Debug.Log(SelfUnit.OwnerPlayerId); // will print player id of the unit owning player.
  }
}