In order to record this information on the user registration page you will need to do the following:
First you will need to modify your database to include this extra column in the users table.
The next thing you should add in the form field into the user registration form. This is the input that the user will enter the company details into.
Next you will want to update the insert record server behavior on this page. This is done with DataAssist. In this server behavior you will just want to update the bindings for the columns. Select your new column you created and then using the lightning bolt icon select the new form element you added.
This will get you to record this new information into your db for that user. You will also need to alter the profile page to have it be updatable. On the profile page you will need to add in the form element, then update the update server behavior just like you did on the insert page.