You put the engagement ring on the left ring finger. No wedding band at this point. As the others said, you can buy a set, or not. What we did was buy wedding bands later after the fact. You will be able to find a band that fits the ring you choose. But some people like to get a wrap, which actually fits around the ring... I would start someplace like Shane company or another jeweler. Tell them you want to surprise you girlfriend with a solitaire. Buy the diamond you want, and have them set it in a plain ring. Ask them if she wants to come back and pick a set, will they refund you the money of the ring and let you put the diamond in the set she wants.. Shane Company I know will let you do this.. You still have the element of surprise with the ring, and she can make it her own afterwards.