The DCS stands for Distributed Control System which is the mean to control your plant operations by using the the distributed (spread across your plant) controllers throught the system with having the Network for communication and monitoring the system.
Read: What is DCS?
ESD stands for the Emergency Shut-Down. This is the way of shutting down the plant in the event of abnormality in plant operation which could lead to dangerous situation. The same is achived by triggering the interlock system which will take the emergency shut-down.
Just to understand the difference between the indications which are local or DCS try to know the difference in the notation/legends of the same.
Read: What is ESD?
There are certain instruments which are just for local indiacation (field) and some are having the DCS indications. The interlock are the safety measures which gets active in the event of an abnormality to save your unit.
Hazop the term is very very broad and a nice experience for any process engineer to have. To know about the technique how Hazop is carried out you can go through some literature available.
I suggest you if your organization has any copy of the Hazop of any facility before go through it and you will come to know. And I hope this will even give you and idea regarding your preparedness for the upcoming Hazop. All the best.
Read: What is HAZOP?
Hope this could help a little.
credits: Padmakar Katre