> >• If we let the cells repair it by themselves, will they not just remake the segment we just cut off?

They will just try to glue the ends back together if you dont add a template for it to insert.

>• If we insert a new gene, how exactly do we deliver it? Does it come with the CAS9 and guide RNA complex? Or do we use another enzyme to deliver it separately?

Usually you supply the template at the same time you supply the Cas9. This can just be DNA. That way when the DNA is cut the template is already available for insertion.