How to understand optimization and performance?

Question

Programming

Hello!
The more I study programming, the more I wonder about: optimization, performance, code protection, etc.
Tell me what literature or courses. So that after passing them I would answer myself the following questions:
- Is the code that I write safe?
- Is it possible to somehow optimize the code, performance?
- What loads my server, site, game, and how to understand how to fix it?
ps: I am writing at night, in the morning I will review what I wrote when I am sober.

Answer 1

1. no. kill it for now.
2. yes, see point 3
3. profilers . at the same time and get acquainted with debuggers, they are relatives.
Hooray, you passed the course! \☺/