How I can preview the ticket form my customers need to fill in before they contact us?
By accessing the ticket form settings
To see your ticket form, follow the instructions in this article: Managing your ticket forms. Only ticket fields that are Editable for end users are displayed in the request form.
By assuming end-users identity
An administrator can take on the credentials of an end user to view and use Zendesk Support as that end user. This allows you to visualize what your customers see when they create a ticket using your request form. For instructions on how to do this, see the article: Assuming end-users.
By previewing your Help Center
The Help Center offers you a feature that allows you to preview changes while you're working on your theme. For more information, see the article: Previewing your help center theme.