RPis are good for education purposes because there's a large community behind. But they are expensive.
Use OrangePi if you need more than two or three later on.
"Installing" is pretty much always the same: Grab an image, write it to an SD card. There are dozens of tools for the job, ranging from dd to Win32DiskImager. As said before, there are dozens of tools out there. Rufus is another widely used option. Haven't used Etcher, but it looks pretty simple (in terms of "noob"-compliance).
Tip: Get a good SD card. Class 10 / UHS from a well known brand like Sandisk, for example. And keep in mind that the SD card will die at some point, they really don't like random writes. Best to avoid them whereever possible, e.g. redirect logs to a rsyslog server, move /var/run and /var/tmp to a RAM-disk if possible etc.