Detecting RATs and other bad things

Hi. I fear that people spied on me on the webcam and I also got an Denial-of-Service attack in last year's December. How do hackers do the Denial-of-Service attacks and how does a person get a RAT in the computer and can hackers spy on the webcam without putting any RATs or with other ways? Are Denial-of-Service attacks done with RATs?

I want to know, because I am also doubting if I got hacked...