Let me enlighten you with an example around maths - in particular, the derivative.
So, what is the derivative? Well, you multiply by the power and subtract one from the power, right? If the derivative equals zero, you have a stationary point! And if the derivative is negative, the graph goes down, and if the derivative is positive, the graph goes up!! Man, you could answer any question with this kind of knowledge!!!
... But, you've managed to define a bunch of different scenarios where knowing the derivative is useful, without actually TELLING ME what the derivative is. Honestly, it's a really simple idea - the derivative is the gradient of the tangent to the curve. We can mathematically define this as the gradient between two points, and then slowly make the distance between those two points (take the LIMIT to) 0. If you understand what that means, and can interpret it well, you have a conceptual understanding of the derivative.
But that's too easy, yeah? What about DNA.
In DNA, the four bases (A, T, G and C [lel for never learning their actual names~]) are only seen in one pair - G with C and A with T. So, if you're ever given a one sided strand, you can find the other! Why, though? Because the textbook told you!
Wrong. They bond that way because they're connected by powerful, polar bonds - hydrogen bonds, to be precise. As such, to create a more stable connection, they only bond in those pairs. The reason those pairs are the most stable is because of the number of polar ends - G and C have 3, A and T have 2.
Okay okay, that's sorta obvious - we can get trickier, though. Let's look at an electric cell. Electrons flow from negative, to positive. Because that's the way electrons move, durr. They don't like negative, so they go to positive!
... But then, why don't protons move around? I mean, we can see the compounds in the cells act as lewis acids or bases, so wouldn't that also imply in aqueous batteries that protons could go flying around? Well, that's because electrons are smaller and WANT to move around. Even in reaction mechanisms, we only consider the electrons forming and creating bonds, because protons are just so heavy. So, we see the electrons go from negative to positive because they're so much lighter than the protons, so they move first, and that lowers the net positive charge, so all of a sudden the protons can't move to balance it out, because they're hitting a net zero and becoming happy.
THIS is what we mean by conceptual understanding. Not just memorising random facts to answer questions - being able to rationalise those random facts with your theoretical knowledge.
[note: used entirely science/maths examples because I feel too much people don't think conceptual understanding can be obtained in these topics, but they totally can, and you really should venture to understand the conceptuals in STEM subjects as well!]