Add/Remove Fields: Select a field in the listing on the left and click the Add button, or double-click on the field name to add it to the selected field list on the right. Dimensions and metrics are managed separately. You can add up to 8 dimensions and 10 metrics in a query.
Deprecated: By default, deprecated fields are hidden but they can be included by selecting the check box. Since the Data API is in alpha status, expect some fields to be changed/deprecated.
Descriptions: Selecting any field will show the associate API field name and description at the bottom.
Filter: to filter the list of dimensions and metrics, simply type a few characters into the filter box provided. The filter can match the display name or the actual API field name.
Update: download the latest dimensions and metrics available, plus any custom dimensions and metrics for the selected property.