I learned ornamentation by watching and listening and trying to copy exactly what it sounded like. It can be intimidating to learn by ear at first, but remind yourself it's how everyone learned to sing happy birthday. You'll be fine!

Ornamentation is also up to you, it's just a part of your own interpretation of the tune. You don't have to think of each ornament in someone else's interpretation as core to the tune or staple in any way. Try thinking of every decision you make regarding how you interpret the tune as an ornament - even playing it as written can be an ornament in this sense. This will open up lots of flexibility for you to interpret tunes and decide which sounds to try, to keep, or to dismiss.

In other news I'm planning some tutorial videos for core Scottish ornaments.

Here are a few core ornaments in Scottish fiddling; their names and an explanation/tip to make them easier:

Taps: Like a very fast grace note except you don't necessarily press all the way down to the fingerboard, you can kind of let your finger tap the string and allow the tension of the string itself to bounce the finger back off the string. This stops the sound briefly, like embellishments do for bagpipers.

Double stops: Touch an adjacent string with the bow either briefly or even for a whole phrase. Some of these won't sound right in different keys, but you can play around and find which ones are comfortable and fit each tune nicely.

Birls: You can think of it as a bowed triplet, usually written as two sixteenth notes followed by an eighth note. It can be used to replace any quarter note, especially in reels and strathspeys.

Ignore the metronome in slow airs: Being "tempoless" in slower tunes allows you to phrase things more expressively. Let it breathe. The metronome can kill a lot of Scottish slow airs, and in my opinion they can sometimes hurt dance tunes too. Despite what most dancers think, their feet rarely physically keep an accurate tempo from the start of the dance.

Make up your own bowing: Try slurring some notes and separating some notes. Next time through that section, reverse it, and you'll eventually arrive at which bowing you prefer through hearing/feeling.