A more thorough explanation:

Definition:

Voluntarily, adv. - Doing something intentionally and without being forced or coerced.

Examples:

• She voluntarily offered to help with the project.
• He voluntarily donated money to the charity.
• The suspect voluntarily turned himself in to the police.

Explanation: When someone does something voluntarily, it means they are doing it because they want to, not because someone is making them. In the examples given, the person offering to help with the project, donating money to the charity, and turning themselves in to the police are all doing so of their own free will. They are not being forced or coerced into doing these things.