Download
Etcher
Download the latest image for your version of mintyPi (you do not need to unpack it)
Insert SD card in to computer
Open Etcher
Make sure it is the correct SD card in the middle
Open and select the image you downloaded
Flash
Bonus steps if you want to use WiFi (BEFORE PUTTING IT IN THE SYSTEM):
When completed flashing, take the SD card out of your computer and plug it back in.
If you are on Windows, DO NOT FORMAT THE SD CARD. Just close the window or hit "Cancel"
Open the boot drive
Open "wpa-supplicant.conf" in something other than Notepad or Wordpad (Notepad++ is a good free alternative).
Insert your WiFi details and save. Use a 2.4 GHz network as 5GHz will not work.
Eject SD card safely
Take SD card out of your computer and put in mintyPi.