The Remington 870 is a fine gun. 12 gauge really is a very versatile gauge. If you haven' t shot at all before, (or very little), start off using lightly loaded " target" ammunition. These loads will provide the least amount of recoil. They will allow you to become use to your gun without pounding you as hard. With a little experience 12 gauge recoil is really not severe. (A less expensive alternative to the " real" target ammo is the very lightly loaded game loads....ie. discount ammo, by the major manufacturers and packed 100 per box.)

After you have become accustomed to the recoil and a little desensitized experiment with different loads to match your needs. Things like patterning your gun....sighting with slugs....and the use of buckshot.....are all covered in great detail at many different sites on the web. A good place to start looking is:
www.chuckhawks.com then go to firearms...then shotguns...and look at the menu of information items. There are many other sources as well.

Good luck with your decision...wishing you much success!