How do I know what is my special mouse button doing and how do I change it?

I have a mouse, Havit model ms1020. It comes with two customizable buttons, but the proprietary software to change them does not work. It already comes with two preprogrammed functions, one of them is a back button for webpages and the other one changes which screen is focused. There are differences between the screen focus button and just left clicking the screen. For example, full screen programs that minimize if you left click another window won't do it if I use this focus button. I tried many keyboard testers and none of them recognized what is this function. Searching for what it is retur

Question by Atsignc on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.