English and Scots are "sister languages" they say (or so I read) in that they started out more or less together but went their separate ways over the years. That means that some words are exactly the same; some words are a little different; and some words are totally and completely alien-sounding.
An American listening to Scots, or someone speaking English with a Scots accent, is never quite up to speed. It SOUNDS like the person is speaking English, but... no. Not the kind of English (most) Americans can pick up without a lot of repetition. In fact, I think you have to live in the region for a while to start picking it up.
To make matters worse, there are variations in words and speech patterns all over Scotland. Edinburgh is different than Glasgow and Southwest is definitely different from Shetland or Orkney. Here is a short example from Caithness. This you will hear in Dounreay and John o' Groats. Try to pick it up.
Here's Edinburgh. I got this pretty easily, although it took me a while to pick up the father's trade of "joiner." At least I think that's what's being said.
Here's Glasgow (1) and Glasgow (2). I couldn't pick this up at all. I felt I was basically listening to English... and yet...
Speaking Scots is NOT the same as speaking English with a Scots accent, though.