Most people do not need a master’s degree.
That being said, however, there are several career fields where a master’s degree (at least) is required.
If your chosen career calls for a master’s degree, you will need to prepare by earning your undergraduate degree, preparing for and taking the graduate entrance exam, applying to graduate schools and, finally, working your way through the graduate classes where, at the end, you will hopefully have completed your master’s degree program.
Master’s degrees are pretty much required in fields such as Business (MBA), Education (Doctorate), Psychology (PhD) and several others. Whether or not you continue on with your graduate studies will be up to you and your career. Good luck to you.