I find it hard to understand the JavaScript I downloaded from colorlib

I downloaded a template from colorlib. After tweaking it to my taste , I made a beautiful portfolio. The thing is I always endeavor to read the code again so I understand why so so and so worked . I tried reading the JavaScript, it is impossible it is over 20,000 line of code , while there is another JavaScript file that’s just 300 lines and seems relatable to the html and css . Please can someone throw more light on the js