I hava a big form and when a user fill it I need to create a new user in Wordpress from there.
Its posible to create and user from the frontend and add some custom information?
Yes, yes you can.
The relevant functions to do this are:
You'll find examples on how to use those functions, and links to more possibly relevant functions. Use these functions in your form handling code on submission, make sure to escape all values entered.
Or if you're looking for a top to bottom tutorial you can check out this one: http://www.cozmoslabs.com/1012-wordpress-user-registration-template-and-custom-user-profile-fields/
There are also plugins that solve this problem.