I am running V QGIS 3.2.3. I have found some answers on here how to do this but in previous versions. Is there a simple way to calculate/Add Xy or utm coordinates to the attribute table?
Probably the easiest solution is the "Add geometry attributes" tool from the Processing Toolbox.
Processing> Toolbox> Search for Add geometry attributes.
It will create new columns. For polygons and lines you will have to decide what X and Y you want to add, for example centroids.