There isn't really a fixed reference for dynamics, in the sense that you can use some sort of measuring device to check you are "doing it right".
If you don't have any reference point at all (e.g. find another keyboard player and ask them, if you don't have a teacher) you could try this approach:
First, try to play as quietly as possible, while still making all the notes sound at a uniform volume level. Call that level "pp". Then, play as loud as possible, and call that "ff". If you are playing an acoustic piano that isn't a concert grand, you will probably find that you can hit the notes hard enough that the sound doesn't really get louder, so back off from that situation. (On the other hand, if you ever get to play a Steinway model D, you can hit the keys with the force of a boxing punch behind your hand, and the Steinway will just play the notes as if to say "OK, you can hit me harder than that if you want"...)
Then divide the dynamic range into equal increments between "pp", "p", "mf", "f", "ff" by ear.
Some composers often use "mp", in which case insert that as another (equal) increment between "p" and "mf". Some also use "ppp", "pppp", "fff", "ffff" etc - in which case you just have to use common sense. It's quite possible that "f" in one part of a long piece is the same level as "fff" in another part - humans are more sensitive to changes in the dynamic level than to the absolute level as measured by a sound meter.
You will probably find that your minimum "pp" level gets softer as you get more control over your playing, but the "ff" level is more likely to be fixed by the instrument than by your maximum strength. Different makes of piano, and even different instruments of the same make, can respond quite differently depending on how old they are, how much they have been played, how well they have been maintained (or not), the acoustics of the room they are in, etc.
