You are having a form having multiple fields. When you render a form, all the fields renders as a separate field. You want some fields to be shown as a collection of fields visually. As a fieldset.
Field Groups module will help you here.
After installing Field Group module:
- goto your content type.
- Manage form display
- You will see a button on top: Add field group
- Click on it
- Select Fieldset. You can chose other options as well, try setting each one of them and see the output.
- Give a name to it.
- You can create multiple Field groups as well.
- Your created Field Group will be shown in Disabled section by default
- Drag that field in active section
- Drag the field you want into this Field Group.
Now save the settings. And now see your form. It should look like below:
See before and after image to realize the benefit of it.