Welcome to the forums, chemtex.
I believe Ruger includes integral bases/rings with their rifles. As I remember, you'll need a slotted screwdriver to mount them to the rifle's receiver. It's important that the screwdriver tip completely (tightly) fits the slot in the screws. You don't want to damage the screws. I forget what type of screw fastens the rings around the scope: torx or Allen (hex), although Phillips and slotted are possibilities. Again, you need the exact size wrench. When mounting, before you tighten the rings to the scope, shoulder the rifle and set the scope forward or backward in the rings in order to set your eye relief. Make sure the recticle crosshairs are plumb and level also before tightening. Some people use Lok-tite to better hold the mount screws. I don't think it's necessary on a .308. Work the bolt when the scope is mounted to make sure it clears the scope. Typically, a 3-9X scope poses no problems in this regard.
You'll want to boresight the scope. Place a target at 25 yards. Support the rifle with sandbags on a bench or something solid. Remove the bolt. Look through the barrel and aim it directly at the target. Adjust the windage and elevation knobs on the scope until they are centered on the target. Looking through the barrel and the scope's crosshairs should coincide on the target. This will get you on paper at 100 yards, where you do an actual sight-in by shooting groups of three shots. Readjust the scope as necessary.
Good luck. BTW all the gun shops here will mount a scope for no charge and bore sight it also. One shop even mounts a scope to a rifle that someone has purchased at another store, no charge. It's good business. I would think the store where you bought your rifle may also mount it for you.
