installer will ask you if you need to use a proxy to access the Internet. You may or may not depending on the LAN settings but in order to use apt-cacher, you must type the URL

httр://DebianServer:3113/

and then click on the Continue button

Вариант1.

If your Debian system is already running, it is not too late! It can still benefit from apt-cacher during your updates or adding new softwares. All you need to do is to edit the configuration file /etc/apt/apt.conf so that looks something like this:

Acquire::http::Proxy "http://DebianServer:3113/";

Вариант2.

Можно использовать каталог /etc/apt/apt.conf.d/, в котором создать файл с настройками proxy (например 20proxy), в котором прописать:

Acquire::http::Proxy "http://DebianServer:3113/";
Acquire::::Proxy "true";