Understand the corresponding basic concepts, theorems and axioms. Can do basic problems. These problems are solved according to axioms, definitions and theorems. Difficult problems are like building blocks and piling up basic problems. The so-called "problem solving ideas" are just some problem solving methods and conclusions. If there are three ways to go, and the first two can't, then you can only take the third one. These methods and conclusions are summed up by myself or teachers and books.

Doing more questions is to understand and master the "basic" concepts and theorems.

Natural science and mathematics are very strict subjects. Therefore, "concept" is particularly important.