Thank you for contacting us and I'd be happy to assist.
Any text added in the "Description" of the custom field settings is only shown in the post/user/taxonomy edit screen in the admin area. It doesn't show in the front-end Toolset Forms.
To include some additional text/description in the front-end forms, you can switch to the expert mode and manually add it with the field, as shown in the attached screenshot.
If we switch to expert mode then ALL the structure changes. We DON'T want to work in expert mode.
Therfor, please add the following description: "Geef het volledige adres (straat, huisnummer en plaats) om uw registratie te kunnen verwerken." to "Adres van de woning" at hidden link AND to "Adres van de eigendom die u wilt verkopen" at hidden link.
If you don't want to switch to the form's expert mode, then the only alternative you have for showing some additional text or description is through the 'HTML content' field.
( screenshot: hidden link )
You can add a new 'HTML content' field above or below your target field as needed and then add your text in that.