1.The first method is used when data is already available with the external systems like local filesystem, HDFS, HBase RDD can be created by calling a textFile method of SparkContext with path / URL as the argument.
scala> val data = sc.textFile("File1.txt")
sc is the object of SparkContext
You need to create a file File1.txt in Spark_Home directory
2.The second approach can be used with the existing collections
scala> val arr1 = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
scala> val rdd1 = sc.parallelize(arr1)
3.The third one is a way to create new RDD from the existing one.