How we make the e.r. diagram of a company having four depatments
1)-H.R.
2)-marketting
3)-accouting
4)-I.T.

May I refer you to the guidelines on homework help here:

https://www.askmehelpdesk.com/arts-literature/announcements.html

You can work out your diagram save it as an image file and attach it to a reply for us to look at and critique. But please don't expect us to do the work for you.