Where can we implementthe event receiver? I am new to the SharePoint so please guide me! Thanks!
Event handlers are something "similar" to the triggers databases. If we imagine a list as a table, we can imagine that an event is a trigger.
Then you can create a business rule associated with the creation, modification or deletion of an item.
You can also create events associated with other actions such as creating a site. A good way to generalize is to associate with content types, rather than list.
They are created with Visual Studio C #.