History explains some of that:
A "Bel" (named fro Alexander Graham Bell of course) is a factor of 10 in power - 10 watts is one Bel greater than 1 watt. So Bel = log10(power ratio).
A deciBel is a tenth of a Bel, so dB = 10*log10(power ratio).
Power is proportional to voltage squared if the resistance does not change, so dB = 10*log10(voltage ratio squared) = 20*log10(voltage ratio). That's why logs are so useful, exponential powers turn into multiplication in the log-world.
Power is also proportional to current squared if the resistance does not change, which you can remember with "twinkle twinkle little star / power equals I-squared R".
DO NOT use the second verse "little star up in the sky / power equals R-squared I" - you will flunk the test as many before you have done!
More historical nonsense - current is I for Intensity, voltage used to be EMF for Electromotive Force, E for short. Mostly people use V for Voltage and let the history go, but so far I remains with us. ... yes, we no longer let the Force be with us, just the Intensity. Kind of sad.
