Basic meaning:
* "A strong work ethic is fundamental to success in any field." (It's essential, a core principle)
* "The fundamental principles of democracy include freedom of speech and the right to vote." (Basic, underlying ideas)
More specific uses:
* "The fundamental particles that make up atoms are electrons, protons, and neutrons." (Basic building blocks)
* "He had a fundamental misunderstanding of the instructions." (A very deep misunderstanding)
* "The changes were fundamental to the company's future success." (Major, essential changes)
Figurative usage:
* "Her sense of justice was fundamental to her personality." (A deeply ingrained characteristic)
* "The fundamental truth is that we all make mistakes." (A basic, universally acknowledged fact)
Remember that "fundamental" implies something essential, foundational, and usually difficult to change.