You will need to purchase some metal corners whether 90 degree or bullnose. You will need to float out the wall to make it nice using an all purpose joint compound or a fast setting compound available in 5,20,40,60,90,120 min. This is the amount of time you have to work withthe product before it gets hard. You will need a 14 inch taping knife and a 14 inch pan. Both available at home centers. It is an art to make look like it was meant to be. Depending on the texture of the walls this may prove to be the most difficult. And may want to consider hiring a pro. Whether you have a skip trowel or spray texture. Drywall pro's are usually not that expensive if all they have to do is texture. Visit the link below http://www.dietrichindustries.com/products/pdf/133_134_135_DMF07.PDF
DIY Drywall Finishing - Setting-Type Joint Compound
Hope this helps, be patient, use the right products and don't be discouraged.
Post a comment on my site at 911handyman.com