Time4Tea: Hi there and congrats on making the switch to Linux! Give it a chance and you won't be disappointed. To help with your questions:
1. GOG Galaxy, as far as I know doesn't run in Linux. Although, like most Windows apps, I believe it should be possible to run it in Wine, if you really want it (for installing/running Windows games). I personally don't use it. Instead, I download the offline installer files from the library pages. For Linux native games, you should be able to download; set the executable bit; and then run the script, which will unpack and run the installer app.
To set the executable bit, you need to run the following command in a terminal (on the file you downloaded): chmod +x [filename]
Files in Linux have a special file permission 'flag' that has to be set to allow them to be executable. That and the robust file Linux permission system is one of the things that makes Linux safer and less prone to viruses/malware than Windows.
2. The Arch wiki is an excellent resource that gives detailed tips on how to set up and use a wide variety of subsystems in Linux. You can easily google it, for example if you google 'arch wiki printers', it will have a very detailed page on how to set up and configure printers. Although your specific distribution (Mint) may be a little different, most Linux distros are basically variations on a theme. The Arch wiki has a very good page on
Wine, which tells you in detail how to set up and use it. Once you have it installed and set up correctly, to run Windows games it should be more or less as simple as running 'wine [executable filename]' from a terminal.
Ignore the section in the Arch wiki on installation (because you are not using Arch Linux). To install Wine, you will need to find and install it using the Mint package manager. Mint should have a graphical package manager somewhere, if you poke around. I don't use Mint myself, but it seems to be based on Ubuntu, so I would guess it will have the Synaptic package manager application somewhere. The package manager being used is one of the main things that distinguishes the different Linux distributions.
Otherwise, there are many good guides on the web that cover how to do things in Linux, such as basic use of the Unix terminal. I hope this helps and let me know if I can help further.
In general, how easy is it to get Windows stuff running. Its a question I often ask myself if I was to look at Linux. Bear in mind that I have perhaps 30years history with Windows, and some 15tb of games, mods, emulators, files, pictures, programming languages, tools, etc. built up over that time. Would it be necessary to go through compatabiliy, setup procedures etc. to get all this running, or does everything run through Wine?