i am trying to save as much money as i can so i want to know if i can put this dent in from the inside or should i just pop it with a dent puller it right behind the front door and the other is a broken part under the tail light do i need to fiberglass it or can i just replace it here are the pictures

 

For the dent, I would use a stud puller. It comes with copper studs that get spot welded to the outside, and you use a slide hammer to pull them out. They work awesome and you don't have a bunch of holes to weld-up afterward. This is the one I have used Stud Welder Dent Repair Kit

For the rear panel you can do a good repair with fiberglass and filler. Or just get an entire panel from you local wrecking yard.