I installed mailman3 on debian through the command:
$ aptitude install mailman3-full
does it need to do further config
As usual, Mark beat me to it. I have some advice to add:
First, look for /usr/share/doc/mailman3/README.Debian or a similarly named file. I would expect to find documentation explaining how to get started, specifically for the standard Debian setup, there.
You may get an answer here, so check back in a couple of days, but as Mark said, since a Debian package is supposed to be configured through the package manager, this is properly a question for a Debian channel.
Unless you are sophisticated in installing software and know your Debian system well, DO NOT try to follow those instructions by yourself. Mixing our instructions with a Debian package install may create a big mess.
tl;dr: Mailman's generic documentation assumes a "vanilla Unix" system, and does not necessarily conform to Debian's interpretation of the Filesystem Hierarchy Standard and other parts of the Linux Standard Base. There is no guarantee that Debian's package corresponds to the version described in "latest", especially not in locations of various files. There is no guarantee that Debian's configuration of the webserver looks anything like our generic configuration, which is similar to the real configuration of the Mailman 3 server we use.
or it is already well configued to use? If yes, how to visit the frontend page?
These are also Debian questions, and should be answered by the resources mentioned previously.