A P4Web Helper is a program that runs on your local machine to manage files in your Perforce workspace. (Compare this to a P4Web Viewer.)
With a P4Web Helper program running, you can use your Web browser to run Perforce commands and work with files. A P4Web Helper can sync files, open files for add, edit, delete, etc., resolve files, submit changelists, and so forth. Your P4Web Helper must be started up and running on the machine where your workspace resides. For information on starting up a P4Web Helper, see How to Start P4Web.
Only you can use your P4Web Helper; access to it is protected by your Perforce password. For more information, see Passwords and P4Web.