With form templates, you can flexibly set up forms of the item create, view and edit pages, add new buttons and widgets, and use scripts.
To add a new template, go to the tab of the form that you want to set up and click <Default>.
To edit an already existing template, go to the Edit tab and click <Default>.
The page for adding a template will open. It has two tabs: Template and Settings.
Template tab
On the Template tab, you can edit the form title, change buttons or create new ones, add widgets and properties.
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The form can be made dynamic. This means that the fields on the form will be shown or hidden, depending on the data entered by the user. You can read more about dynamic forms in this article.
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Adding a property to the form
In the right panel, go to the Properties tab. It contains app properties that you can drag onto the form. It also displays the properties of the widgets used to configure them. 
You can drag and drop properties both on the main area of the form and on the side panel. In addition, you can arrange the properties in the Element layout widgets for convenience.
Adding a widget to a form
A widget is an interface element for such actions as uploading a file, showing instructions, displaying messages, user lists and so on. Widgets allow you to create the most convenient form for work, to visually place fields, add buttons, and configure user interaction with the interface.
To add a new widget, drag it from the Widgets tab on the right panel.
To add a widget to the side panel, drag it to the side panel or click +Widget.
Read more about adding widgets to a form in this article.
Context tab
This tab displays the variables used in the widget settings. Most often they are needed in order to configure the behavior of the widget, for example, to show a pop-up window when the cursor is hovered over a certain area of the form. This is configurable through scripts. You can read more about working with them in the Scripts article, where you will also find their use cases.
Reusing form template
The template that you have configured for the Сreate form can also be used for the Edit form.
Simply click on the «Default» link and select the form in the drop-down list.
Such elements as widgets, buttons, and headers added to the Create form will now also be displayed on the Edit form.
However, keep in mind that if the list of fields featured on the Edit tab is different from the list of fields on the Create tab, then the fields on forms will also be different even though you are using the same template.
If you want the fields to be the same, go to the template settings and delete the «Standard item form» widget, since it is the one that displays the fields from the Create and Edit tabs.
Instead, drag the necessary fields from the Properties tab of the right pane.
With such settings, both the Create and Edit forms will feature the same set of fields.