I need to upload/import a list of users via excel to a visual force page. The page has a lookup now to add each member manually now. The requirement is to add more users (say 100) at one go. how to achieve this functionality

trigger to create an contact wherever the account is created for specific set of users(say i have a set of 5 users and whenever they try to create or update an account the contact should be created or updated accordingly)

Trigger to update account field