To see entities with queries, go to the Graph Explorer with an interactive sandbox.
Entities
Entities define the schema of the subgraph, and represent the data that can be queried. Within each entity are sets of fields that store useful information related to the entity.
Each entity is defined with a value type, which will always be a base AssemblyScript type, or a custom type provided by The Graph's custom TypeScript library.
To get a snapshot of past state, use The Graph's block query feature and query at a previous block. See this post to get more information about fetching block numbers from timestamps.