Hello Brian.
Modern RADIUS implementations use UDP port 1812 for authentication and authorization, and UDP 1813 for accounting. Older implementations used 1645 and 1646.
Here’s what freeRADIUS uses
So what you would do is specify the ports as 1812 for auth/autz and 1813 for accounting so the device knows which ports to use.
The ports you specify here should be the same as the ones you’re using on the RADIUS server. Most RADIUS servers should use these ports by default but just like with anything else, you always have the option to change them 
So in summary, RADIUS implementations will typically use 1812/1813 these days, so you can specify these ports in the command. However, these ports can be changed and if you’re unsure what ports is the RADIUS server using, you’re always free to log into it and check. What’s important here is having the ports specified in the RADIUS configuration and on the RADIUS server the same.
David