A buffer, generally and inaccurately speaking, would make a "copy" of a signal that can be used in the rest of the circuit without affecting the original signal. It does so by presenting a high-impedance input to the original signal so to minimise its effect on it and it normally has a very low output impedance. The simplest circuit these days for a static DC-coupled signal would be a non-inverting operational amplifier with unit gain:
|\
Aref --- |+ \
| \______ buffered out
| / |
|--|- / |
| |/ |
|___________|
get an opamp that can operate from a 5V power supply and you should be good.