WP-Piwik Setup

you say:
To enable Piwik statistics, please enter:
your Piwik base URL (like http://mydomain.com/piwik) or your Piwik server path (like /var/www/mydomain.com/httpdocs/piwik/)
your personal Piwik authentification token. You can get the token on the API page inside your Piwik interface. It looks like “1234a5cd6789e0a12345b678cd9012ef”.

then there is a box labeled “Piwik URL (REST API)
is this where you are supposed to put the url path where Piwik is loaded?
If so, why do you call it “Piwik BASE URL” above and here you refer to it as “Piwik URL (REST API) ??
Confusing.

And does it matter if you list your url with the “www” or not?
example
http://www.mydomain.com/piwik
vs
http://mydomain.com/piwik

Also Expert settings:
What am I supposed to set for the “user agent”?
PHP is default ()
What would happen if I selected “WP-Piwik” instead of PHP?

thanks

https://wordpress.org/plugins/wp-piwik/