You can map multiple form fields to the description area of your Zendesk tickets created through form submissions.
In the Settings → Application section of your online form, go to the Zendesk app and hit Customize to open the customization lightbox.
Next, click on the text area from Description and use the dropdown displayed below to add the form fields you want. Select the field and click on Add to include the input of the field in the description area.
Repeat the steps each time you want to include another field from your online form. Exit the customization lightbox through the Save button.