Short Answer: DataFrame API was introduced In Spark 1.3 release. There has been a lot of changes at a rapid pace that are made to Spark including changes and additions to core APIs. One of such important change made is around the representation of data sets. Spark 1.0 version used the RDD API and new alternative and incompatible APIs such as DataFrame API was introduced in Spark 1.3 release and Dataset API in Spark 1.6 release.
If you wish to learn Spark, you can enroll in this Apache Spark Training course by Intellipaat that offers instructor-led training, hands-on projects, and certification.
Also, watch this video on Spark DataFrames: