AQL is constructed as a set of interconnected domains as displayed in the diagram below. You may run queries only on one domain at a time, and this is referred to as the Primary domain of the query.
Currently, the following are supported as primary domains: Item, Build, Entry, Promotion and Release. i.e., your queries may be of the form: items.find(...), builds.find(...), archive.entries.find(...), build.promotions.find(...) or releases.find(...).
You may use fields from other domains as part of your search criteria or to specify fields to display in the output, but in that case, you need to follow the conventions described in Using Fields.