The web part provides a way to create a password reset page with a custom design that can be used instead of the default system page. The URL of such a page must be entered into the Reset password page setting in Site Manager -> Settings -> Security & Membership -> Passwords or into the Reset password page URL property of individual Logon form web parts. Once assigned, the links in the confirmation e-mails sent as a reply to password reset requests will lead to the page. There, the web part will automatically process the query string parameter and allow users with valid requests to change their password.
Help URL: http://devnet.kentico.com/docs/webparts/index.html?ResetPassword_overview.htm