The opamp is short for operational amplifier. You can read more about those here http://www.allaboutcircuits.com/vol_3/index.html in section 8. And this is your thread now so feel free to post again if you need some help.
Standard op-amp buffer circuit is: input to the IN+, IN- wired straight to OUT and then obviously OUT is your output.
Look for a single supply op amp to simplify the power supply requirements.