Difference between CSR creation and create domain certificate

I'm a CA admin and I'm new to this field, Can any one explain the below scenario and explain the difference between them.

Scenario 1 - System Admin creates a CSR file and give it to me... I will generate a certificate by CSR file and issue it back to System admin

Scenario 2 - System admin select the option " create domain certificate " instead of CSR file.

What is the difference between them can anyone please explain this?