nmap command help required

Thanks for that, i’m kinda new to linux and was hoping to find just that.
1 more question though: why the “s” in “sed s/,$//” ? i know the comma and the slash are escaped with the “/”, $ is end of line, but still can’t figure out what the “s” is for. is it just to prevent it from reading the first “/” as an argument? like it could in fact be any letter?