After you have logged in as the dedicated user for Hadoop(in my case it is hduser) that you must have created while installation, go to the installation folder of Hadoop(in my case it is /usr/local/hadoop). Inside the directory Hadoop, there will be a folder 'sbin', where there will be several files like start-all.sh, stop-all.sh, start-dfs.sh, stop-dfs.sh, hadoop-daemons.sh, yarn-daemons.sh, etc. Executing these files can help us start and/or stop in various ways.
start-dfs.sh, stop-dfs.sh and start-yarn.sh, stop-yarn.sh: Same as above but start/stop HDFS and YARN daemons separately on all the nodes from the master machine. It is advisable to use these commands instead of start-all.sh & stop-all.sh.
If you want more information regarding Hadoop the check out this video tutorial that will help you in learning Hadoop from scratch: