The parts
The address is read the way your browser reads it and split into its protocol, host, port, path, query and fragment, with the origin (protocol, host and port together) at the end. A user name or password written into the address is shown too. Where no port is written, the usual one is filled in and marked the default: 443 for https, 80 for http.
Query parameters
Everything after the ? is listed as a table of names and values, decoded, so q=hello%20world reads hello world and a + reads as a space. A name that appears twice, such as ?tag=a&tag=b, gets a row each time, in order, so tracking tags and filters are easy to check.
Questions
Why does it say the address is not a full URL?
It needs the protocol at the start, such as https://; example.com/page on its own could be a file path. Add it and the address is read.
Can it build a URL with UTM tags?
Not here. The UTM Builder adds campaign tags to an address and keeps the query it already has.