Door installation is not a complicated process if you have the knowledge. First, one has to measure the rough door openings, and most inexperienced persons are going to fail at the inital step. The expendable materials like foam and tools etc. to be prepared in advance. Then you assemble the door frames unless you bought them pre-hung. Then you have to mount the hinges. Then it’s time to install the door frames and to fill the gaps with foam. Now prepare the door locksets and install the handles. Actually, my advice is to turn to a professional; thus you can be sure the door size is right etc.