WHAT ARE THE STEPS AND THE AMOUNT OF TIME NEEDED TO INSURE THAT THE ROAST IS DONE?
What type and size of roast? Are you using a recipe? You can find many on this site or by generally googling pork roast.
Google is your friend
I'll disagree on the google thing. Just because it's on the internet it must be true, right?
For say, a pork shoulder roast I would lard it with garlic slivers and rosemary. Hopefully there is still some fat cap on there. Rub it down with olive oil and coarse salt and roast at 375F. Depending on weight, time in the oven can vary. You'll want an internal temperature of 140F. Tent it and let it rest for 10 to 15 minutes before carving. It should still be a little pink. That's a good thing.
Cuban Roast Pork Shoulder I marinate overnight in mojo made with sour oranges, oregano,olive oil and garlic.
Then cross hatch the fat and lard it with garlic and oregano. Slow cook at 375F also. Takes hours.
Comes out extremely tender.