I recognize that a BJT is likely my best choice for a buffer, but there are so many configurations for transistors and caveats like biasing that I always get confused when I try to learn about them. For instance, in the diagram of a common collector transistor, with Vin at the base, V+ at the collector and Vout at the emitter, I don't get what the emitter resistor that is sent to ground does or what value it needs to be. I know this is simple stuff, but I haven't worked with transistors in the past.