How do you add a click button to add more fields, like the ones already exsisting on a form?

Is this possible? So if a client needs to fill in more than there is available on the form can they click a button or something to add more?

Is this possible with jotform?

Yes, this is possible here in JotForm. You can use the Configurable List widget or the Infinite List widget.

Configurable List widget - [Demo form]

Infinite List widget - [Demo form]

Here's a related guide: How-to-Set-Up-the-Configurable-List-Widget

Hope that helps. Thank you.