Here is an example /etc/apt/sources.list after a default Debian 11 install but generally this applies to almost any Debian.
# deb cdrom:[Debian GNU/Linux 11.2.0 _Bullseye_ - Official amd64 NETINST 20211218-11:12]/ bullseye main
#deb cdrom:[Debian GNU/Linux 11.2.0 _Bullseye_ - Official amd64 NETINST 20211218-11:12]/ bullseye main
deb http://deb.debian.org/debian/ bullseye main
deb-src http://deb.debian.org/debian/ bullseye main
deb http://security.debian.org/debian-security bullseye-security main
deb-src http://security.debian.org/debian-security bullseye-security main
# bullseye-updates, to get updates before a point release is made;
# see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
deb http://deb.debian.org/debian/ bullseye-updates main
deb-src http://deb.debian.org/debian/ bullseye-updates main
# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.
deb http://deb.debian.org/debian/ bullseye main
deb-src http://deb.debian.org/debian/ bullseye main
deb http://deb.debian.org/debian/ bullseye main non-free contrib
deb-src http://deb.debian.org/debian/ bullseye main non-free contrib
Now you'll have access to additional, often missing or newer packages than the standard main Debian repos provide.
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