Once you’ve configured for your repository, download and update the indexes of packages by running the following command. Run this every time you add a new package:

$ sudo apt update

Once this has succeeded, you can use apt and all related tools to install your private packages:

$ sudo apt install package-in-gemfury
...
The following NEW packages will be installed:
  package-in-gemfury
...
Setting up package-in-gemfury (0.1.0) ...

apt is the newer CLI for accessing APT functions in Debian-based packages. If you prefer or in older versions, you may use apt-get instead.