Questions regarding Guix as an OS, Guix as a package manager, and the wiki itself.
GNU Guix (or simply Guix) is a liberating, dependable, and hackable GNU/Linux distro configured using Guile Scheme. It is liberating because by default it uses only free software, and the Linux libre kernel. It is dependable because it is reproducable, supports rollbacks through "generations," and has transactional upgrades (as well as much more), and is hackable because it has Guile Scheme APIs for the entire system and packages.
More practically, this means that Guix is configurable in your dotfiles (your GNU/Linux preferences, nicknamed dotfiles because they often start with a period) and are reproducable on all your machines. Your configuration can be copied across them all, and kept in version control (such as git).
You can install Guix either as an OS or as a package manager in a foreign distribution of GNU/Linux. There are benefits to both, however if you truly want to reap all the benefits of Guix, you should use it as an OS. The choice is up to you.
If installing as a package manager, Guix can be downloaded as a binary from the official website at guix.gnu.org, from your distro's package repositories, or using the shell installer script.
If installing as an OS, you can go back to the System Crafters main wiki page for GNU Guix to see the options between nonguix and normal installation.
Well, you find alternatives! The FSF has a great article about this (written specifically for the COVID-19 pandemic, but always applicable): free software alternatives. For other general things, consider LibreOffice for Microsoft Office, Gimp for Photoshop, Inkscape for Illustrator, and there are many other good alternatives to look for that respect your freedom.
That said, we all have programs that we need for work that aren't free (and if you don't, consider yourself lucky.) Guix System, the name for the OS version, has options for nonfree software, such as nonguix, Nix, and Flatpak.
A declarative configuration is, put simply, when you write out your settings and packages instead of running a command. This allows for reproducibility, and easier management of installed packages. Think of it as declaring what you are going to do before doing it, as opposed to doing it without writing it down or alerting people.
First and foremost, Guix is configured in Guile Scheme, a Scheme (which in itself is a Lisp), while Nix is configured in... Nix. A bit confusing :smile:. Guile Scheme is a full fledged Scheme programming language, which means you can do some powerful things in it. Packages as well as system configurations are written in Guile in Guix. Guile also has more unified commands, while Nix has many for different purposes.
Check out one of the System Crafters channels on Discord, IRC, and Matrix. You can also watch some of the System Crafters videos, read this wiki, or ask in #guix for free and #nonguix for nonfree on Libera.Chat IRC.