how do you get combo list?

where yall get the username and password from ? why does some people crack account soo easily and how can i get the combo list ? did yall just make up any username and password ?

There are many ways to get a combolist.
But the most popular ones are:
SQLi and other exploits
Scraping usernames and bruteforcing the passwords

Using the scraper, with common used passwords

Scraper is the most common