Question on a few steps during install

Hello
After a few hours I finally managed to install the iso on an old desktop.

I do have a question.
During the install there are options to install If I remember
the HTTP proxy

and mirror I skipped these 2 ...are these necessary and why?

if they are can I go back and fix it?

Also Is the user and password also necessary or about security when installing?

I am new at this and this is my first succesfull install.
Thank you!

If you have a simple network and don't have any proxy details you can skip that part.

Mirror lets you choose a repo geographically close to you, unless you are installing a large number of packages and the server your are using is slowwwwwwww don't worry about it.

You need a user name & password. Like many concepts of Quantum Physics just accept it for what it is.

Since the installer is just a plain Debian installer many answers can be found here, the only difference being Linuxcnc packages are installed and a realtime kernel is install as well:
www.debian.org/releases/bookworm/amd64/

With advances in internet connectivity some of these things are generally unnecessary today
A corporate network or ISP might run a proxy server that cached internet content for preserve bandwidth, Commonly requested content would be cached locally. Content is returned from the cache instead of the real source
A network of Debian mirrors was established around the world so you could download large files like ISO's from a server near to you without resorting to  pulling an image from the other side of the world via a slow link (eg via an undersea cable)