How to enable additional Debian repositories?

Question

linux

Good afternoon.
There are three Debian ISO disks.
The system is installed from the 1st disk.
On the other two additional repositories.
How to connect them?
I have tried mounting and then adding to sources.list. At first there was an error that there was no gpg key - I ignored it. It seems to have gone, update works, but it doesn’t see anything from the ISO, it doesn’t find any necessary package.

Answer 1

apt-cdrom add