I want to learn about how apt works & fetches objects from mirrors in sources.list. How can I browse these repositories manually, download them manually & build them manually (not using source and not github, etc...)?
When I want to download a specific version of a package manually with wget, I use pkgs.org. This site basically have an index of all major repositories, and provide many package details.
It supports a solid handful of distros beside Ubuntu (you can find newer packages by installing from Debian unstable for instance), and both amd64 and arm64 architectures.
Here you can browse or search for any package, and you'll get the download link directly.
Take this example with Nano for Ubuntu 20.04.
You get a download link, a list of dependencies, list of files etc. To download this package manually, you just fire wget with the link provided:
wget http://archive.ubuntu.com/ubuntu/pool/main/n/nano/nano_4.8-1ubuntu1_amd64.deb
You can then proceed to do whatever you want with the package.
