@Regina ChristianyI would recommend you to start learning HDFS and YARN architecture first. Once you understand the architecture then you can download our HDP sandbox from hortonworks.com and play around with it.
Please do some research about your domain and decide on what all Hadoop Ecosystems(Hive/Pig/Spark etc.) you need work on and start reading about them one by one.
While learning Hadoop and ecosystems, if you have any doubt, please post it here on HCC. We would be happy to help you! 🙂
All the Best. Happy Hadooping!! 🙂
Below are recommended books which would help you to start learning about HDFS and Yarn
http://www.amazon.in/Hadoop-Definitive-Guide-Tom-White/dp/9352130677/ref=sr_1_1?s=books&ie=UTF8&qid=...
https://www.amazon.in/Hadoop-Operations-Guide-Developers-Administrators-ebook/dp/B009J3I62I?ie=UTF8&...
Hope this helps.