The conversion factor is a fraction in which the numerator and the denominator have the same value (they are equal values expressed in different units), and so the conversion factor is equal to the unit.
Using conversion factors we can go from some units to other equivalent ones with little risk of making a mistake. We just have to multiply repeatedly by successive conversion factors, until we get to the units we require.
By clicking on the corresponding controls in the following animation you will learn to go from one unit to another using conversion factors.
It may seem complicated at first, but once you have learned you will use them all the time, both in Physics and in Chemistry.