ahoy @SrinivasS218965,
Form builder is one of a few options how you can add fields on a table form - either add existing fields that were not yet displayed or create new ones that were not existing before.
You can go to a record of any table, then click the triple line > Configure > Form Builder:
It will open the Form Builder in the current table - in my example I was on the User [sys_user] table so opening FB will open it on the same table as seen below:
but you can either go to different form and open it or to open the form builder from User table but switch it to Company, Incident, ... or any other table as per your need.
Then in this tool, you can easily drag and drop fields, give them attributes (read-only, mandatory) or default values (what value should be selected upon creation) etc.
Similar things can be done from triple lines > Configure > Form Design
or triple lines > Configure > Form Layout
Adding existing fields on a form or creating new one can be done in all three options but if you want to make that field mandatory, it is easier with Designer or Builder where you can create/add a field and directly make it mandatory while in the Form layout you might need to create the field and then give the attributes in extra step not possible to do it directly.
TL;DR Form builder is one of a few methods how to manage tables, their views, fields and attributes. Each of them has some pros and cons, it's up to you which to select.
