DataFrames are a relatively recent addition to Spark. There is thus still a dearth of literature and documentation. The first port of call should be the Scala docs, available at: http://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.sql.DataFrame.

The Scaladocs for operations available on the DataFrame Column type can be found at: http://spark.apache.org/docs/latest/api/scala/#org.apache.spark.sql.Column.

There is also extensive documentation on the Parquet file format: https://parquet.apache.org.