Question

What is the difference between a differential and derivative?

Answer 1

Like I understand that it's something like dy/dx vs dx. But what does that mean?

Answer 2

In simple words, a derivative uses infinitesimal values, which can be represented with limits, as the definition of derivative is:
\[\lim_{x \rightarrow a}\frac{ f(x)-f(a) }{ x-a }\]
Since limits are defined by infintesimals, means that the derivative works with extremely small values.
Differentials on the other hand are defined as an approximation, or more likely the difference between two points in the cartesian plane, for a better example.