As you learn, you will need to always do a check on reasonableness. This means that you understand numbers and units and measures enough to realize when a number is a reasonable value for something and when a number is somewhat impossible or even ridiculous.
Let's say an acquaintance of yours told you that they know this friend who is really tall. You ask how tall and they say he is 5 meters tall. Sound right? Reasonable? No, it is not reasonable at all. 5 meters is about 16 ft 5 in which is way too tall for any human being on this earth. Maybe they said meters and meant to say feet. Certainly more reasonable for a human to be 5 ft tall - but then the whole "really tall" thing falls short of being believable.
True Story: I once had a conversation with a guy who worked on communication towers (antennae). He told me he would climb those really tall antenna towers that you see over in west Austin. They are really really tall - you can see them when you look towards the west with an unobstructed view. They all have red lights on the tops of them for warning signals to low flying airplanes. He changed the bulbs on them. He told me those towers were each a little over a mile high. I immediately told him that he was mistaken and that there was no way those things were 1 mile tall. He argued because some old fart that taught him the tricks of the trade told him the same thing. So nice to pass on totally wrong information from one generation to the next (it's a thing we do). Anyway, they aren't that tall at all. His "mile high" struck me immediately as not reasonable at all - ridiculous. Unfortunately, this argument about height was before the smartphone came along and we had no immediate source to look up the true height of those antennae. BTW, that really just means it was before 2007 (iPhone introduced by Steve Jobs). We parted ways each thinking the other was a dumbass (he was, not me BTW).
So lets have that same conversation here in 2019 with smartphone in hand. He makes his mile high claim. I say no way and pull out my phone and type something like "antenna in west austin"... the very first link is this: West Austin Antenna Farm on Wikipedia. Click the link and read. The tallest of the group is the KXAN tower at 1308 ft. Holy-moly, that is really tall. It's over 4 football fields tall! Damn. I would've been impressed just telling me the actual truth. But a mile? I'm calling bullsh*t on that. One mile is 5280 ft. So that tower is just over a quarter mile high. Not a mile. End of story.
Pay attention to units and numbers. Get familiar with sizing of all sorts of stuff. You should be able to get "in the ballpark" of guessing sizes of things we cover. A molecule is tiny - we know that. A human hair width is also "tiny". But those two things are vastly different in their sizes. Go read up on these sorts of things. I'll point many of these types of things out in class. The idea is to get you to have a feel for the size of the matter that is around you and in you. And... the most important life lesson here.... learn to call bullsh*t when something is clearly not right.