You can first learn what is Big Data and why does it require different kind of handling. You will come across the V's of big data. You will come across some of the most common tools in Big Data world. You will learn that for Big Data the processing can be batch processing or Realtime processing. For the former, you may use map reduce or Spark batch and for the latter you may use Spark Streaming or Strom. You would learn that Map Reduce is part of Hadoop which includes tools like map reduce, hive, hbase, flume, oozie and others. You will learn that persisting Big Data requires nosql databases like hbase, cassandra , mongodb, cosmosdb etc. You will learn that the first two are the columnar databases while the last 2 are key value stores. You can make applications and learn in depth, some of the technologies mentioned here and other big data technologies. This can be a good start.