Firstly, apologies as I'm a newbie and have only been studying GIS for a few months. I am digitising field boundaries and have a field within a field, and am wondering what the best way of representing this in a single layer is, so that the area of the internal field is subtracted from the area of the main field. I have read an explanation about donut parcels but am not sure if this is the right solution for what I want to do? I am using ArcMap. Thanks in advance for your suggestions.
There is an Esri Technical Article on this (don't be put off by it only going up to ArcGIS 9.3.1 because it still applies at 10.1).
Try the instructions there and, if you have any problems, perhaps edit your question to describe the steps you have done and where you may need further assistance.
A quick description is:
If I were you I would use the "cut polygon tool" to cut out that field within a field. After that, you could either delete it or keep it.
Since you are using ArcMap, I think this link is really helpful to your question.
Hope this works.