An applicant can apply for multiple positions by going to "Job listings" on the main application menu. You do not need to enter all your information again. Once you create a profile, you should be able to apply for more than one position by just clicking on the position title, reviewing your information, and by hitting submit to finish the process.
An applicant can only apply for a job posting one time with their account. If they would like to update any information in the application that they have previously submitted, then they can do so by navigating to the Profile tab within their account and editing the profile associated with that application.