C.S.
I take it you are not able to afford a professional(?). I think your best bet would be to purchase a DIY book at the hardware store. Can you hire a handy man?
If not, you can probably do this yourself. We were alone without Dad in the house for the majority of my childhood and we did a lot of repairs ourselves.
You don't mention if it was due to water damage. If so, you will need to remove any mildew rotted wood that may have been caused by sitting water. If this is the case, I really think you will need a professional.
Remove the old insulation and take the numbers off the old insulation and talk to the hardware store about new insulation. Chances are, it is now updated. You should tell the hardware store the size of your home, the location of the insulation, and the outside hi/low temperature in your area.
You will need a utility knife, it is a razor blade with a handle. The knife should be a hardware knife and not a craft knife or you will cut yourself! Cut the dry wall (DW) into a square where it is broken. You will need to cut the DW down to the 2x4 so that you can nail the edge of the DW to the 2x4. Don't forget to remove all of the old nails or they will poke through the DW in time. Insert the insulation and with the help of others, hold the DW in place and nail it to the 2x4, which should be 16" apart. So you will want nails on the edges and in the centers at each beam.
Then you will need drywall tape (really it looks like calculator tape) and puddy along with a puddy knife. Apply the puddy at the seams and scrape ALL of the remaining puddy off with your puddy knife (which comes in different sizes). Sort of like icing a cake and making it smooth. Apply the tape to the seams and puddy again, scraping all of the excess off.
You can sand the dry puddy until it is all one even smooth surface. Prime & Paint!