A good way for buffering one circuit to another to try and match impedances and avoid loading is to use an op amp wired as a voltage follower also known as a unity gain amplifier, which has a gain of 1, meaning what you put in, is what you get out. But has a very high input impedance, which then can take its input from a source and drive some other load, so it acts as a buffer between the two. Check under projects for an RC time constant example circuit
Another way a voltage follower works is with a transistor wired in a configuration with the load connected through the emitter and to ground, this also follows the voltage at the base of the transistor, but with a larger current swing determined by the hfe or beta (gain) of the device selected, with a .7v loss from the original signal, (due to the base-emitter) so more or less it is the same voltage minus the .7v. If a darlington pair transistor was used, these are for current amplification, and are two transistors with their gains multiplied in the one package, this would cause a loss of 1.4v across the base emitter junction compared to the input at the base. This loss could be a problem if say for example, the load requires 12v and no less, and the power supply for the whole circuit is 12v, then the load would only see 10.6v at a darlingtons output, due to the 1.4v loss, a 13v psu maybe required or higher to cater for the circuit been designed. which can have a knock on effect in other areas which may require 12vdc, so voltage droppers or regulators may need to be implemented.