As ice flows over the lanscape, it crushes and scrapes the underlying rock. Small pieces of this rock get caught in the base of the ice, and the ice sheet essentially turns into an enormous sheet of sandpaper. Even though the ice only moves a few hundred metres per year (slower than a snail!), over thousands of years, it shapes the landscape underneath it. Have a close look at the hills around Dundee - they are all elongated in an East-West direction. This is particularly apparent when looking at them from above, for instance in the satellite image below. It looks like a comb has been run across the landscape, scraping all the hills and valleys out in the same direction.
A very nice map is available to scroll through the different glacial feature which have been mapped across Scotland and the rest of the UK: https://shefuni.maps.arcgis.com/apps/webappviewer/index.html?id=fd78b03a74bb477c906c5d4e0ba9abaf