How can I ensure that my code, program, or software is functional and secure?

Following customer's requirements and writing tests by using a framework like JUnit can help code and program, software to be functional and secure. Running tests and coverage can help uncover defects and bugs in the code.

How do I interpret user needs and incorporate them into a program?

User needs are documented as requirements and a software engineer uses the requirements to develop and test new features for the user.

How do I approach designing software?

Designing software involves following the SDLC Software Development Life Cycle. Using SDLC a developer or team can use the specific needs/requirements of the customer to write code and tests.