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!