How to customize default user registration on d8 with webform

Greet the community,
I have a problem with the drupal 8 default registration module. I do not know if I should create a new module or use the existing default module. The form of registration by dedaut not respecting my requirements j ai of which to use the module webform to make one, my problem and that of how I modify the form by default to use my new form definit. Some will say that i have on admin> config> account to add the main fields, there are not the fields I want. Please help me … should I create a new module ??? If not how to use existing so that it fulfill my needs well will help because its will be useful to me

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