Step 1: Motivation
Say you have a voltage source, but it isn’t adjustable and your load requires a smaller voltage. The simplest way to remedy this is with a set of two resistors, which will make up a voltage divider. If you know how voltage dividers work, you will know how a large part of electronic circuits work!
Step 2: How a voltage divider works - an example
If we hook up our load in parallel with R2, we may give it whatever voltage (less than Vin) with good choice of R1 and R2 values.
For example, if Vin is 15 Volts and R1 and R2 are both 100 ohms (as in the attached file voltage-divider.pdf), Vout=15*(100)/(200)=7.5 V. Thus we can get an output of 7.5 Volts from a fixed 15 Volt source!