Voluntarily means doing something by your own choice, not because someone forced you or required you to do it. When you volunteer to help clean up after a school party, you're acting voluntarily: nobody made you do it, you decided on your own that you wanted to help.

The word emphasizes that free choice is what matters. If your teacher assigns you to help clean up, you're no longer doing it voluntarily, even if you don't mind the work. But if you raise your hand and offer to help when no one asked, that's voluntary action.

You might voluntarily share your lunch with a friend who forgot theirs, or voluntarily admit you made a mistake instead of waiting to get caught. A library might accept voluntary donations instead of charging fees. Notice how the word often appears in situations where someone could have avoided doing something but chose to do it anyway. That choice, that act of deciding for yourself rather than being pushed or commanded, is what makes an action voluntary.