How to customize forms in a new application
Do you mean, to save your customizations within the new application?
In general have a look at the doc: https://docs.erpnext.com/docs/user/manual/en/customize-erpnext/customize-form
Also have a look into the following thread to understand, when to use fixtures and exporting customizations: Export Customizations vs Fixtures
If I customize the form, my other ERPNext is similarly or similarly customized.What should I do?
I know that in a production environment it is possible to back up the database and restore it
In a development environment.I can create a new application to customize but I don’t know how
For example, change the number of columns, width, and layout of the form