The below view declares two argument langauge and system user. The view is used to retrieve product id with description via inner join.
When we locally preview the view, we are asked to provide the value for these two argument.
In productive use, it is this @Environment.systemField annotation which takes effect. In open SQL we do not need to explicitly pass value to these two parameters.
See following ABAP code: all products created by Jerry are fetched, although no parameter for user name is passed.
You can verify via ST05 that ABAP runtime automatically fills these two parameter for you: