Pinned data is data about folders etc. to make your browsing better. Cached data is partial data located on your drive to help speed up load times - this value can be changed at any point to none or a lot more.
Left pie chart shows data on your drive and what parts is what. Mostly this chart will be dominated by "to upload" when you have copied data to your drive.
Right side shows how much if your data is located locally vs in the cloud.
You can resize your drive in the drive options located under the left pie chart.