HI @SB21,
If you create a property with an internal name that exactly matches the parameter, HubSpot should pick up the information automatically.
Using your example, if you want to store the source, you’d have to create a custom property with the internal name “source”, and HubSpot should pick up the value “Test” automatically if you include the newly created property as a hidden field in your form: https://insights.frost.com/cs_test?Source=Test
This tutorial by Align.ly is also a great overview.
Hope this helps!