Bug-Bounty is a process where hacking companies, or hackers, act as 'middle-men' to detect bugs in software and address cyber vulnerabilities that organisations are facing. These hackers are then duly rewarded for discovering these vulnerabilities before they become a detrimental security issue.
Get an hand-on approach on hunting bugs. Hackerspoilt does a walkthrough with the tools that he uses when hunting vulnerabilities on Kali Linux.