Add more code to other people's program

Hi,

The program I will fix was developed by somebody else and It is already in Production.

In Dev:

1. From SE38, "ABAP Editor: Initial Screen", I see the "Activate" button, but this is not where I suppose to modify the program

2. I typed my program name in "ABAP Editor: Initial Screen" and get the source code. After I added my code, I only see "Save" button and don't see "Activate" button in the source code screen as below:

I am just wondering do I need to activate the program after the save? if so, should I go back the "ABAP Editor: Initial Screen" to activate the program? If not, does it mean the change is activated automatically in the system?

Your input will be much appreciated