realistically, nobody uses all the units.
eg, decimeters are practically unheard of.
anyway, start measuring things around you. like your fingers, your hand, your ceiling height, that sort of thing. and then remember what those measurements feel/look like. that'll give you something to compare other things to. you can do the same thing with volume measurements and so on.
for example, i found that one of the knuckles on one of my fingers is exactly 4cm long, so i always have that with me.
the brain's actually trying to understand what things are made of, and it's guessing at that based on the light that enteres the eye.
this is why when you pick up a thing outside and take it inside, it doesnt change color (edge cases exist), even though the light that reflects off of it into your eye absolutely changes a lot.