Porting to what ? To Android ? To the web ? To the good old System V ? Or perhaps is it porting from an engine to another one ?
But, anyway, like each engine are different, they also have different way to be ported, what imply that there isn't a "one for all porting tutorial".
In order to, possibly, have an answer, you should explain what you are trying to do. Then perhaps that someone among the readers will know where to find a tutorial for this.