Everything related to Sugar's activities is located in /home/olpc/Activity . Each folder represents one activity and everything that is related to it is present in the proper folder.
Example in HelloWorldActivity.activity:
Once everyfile is in it's due place (follow the tutorial shown on the previous post for more details), one needs to restart Sugar by pressing ctrl+alt+erase. The activity won't appear on the desktop... yet.
But if you go check in the activity list...
... and click the little star, then the icon will automatically be added to the circle on the desktop.
From here on, you can freely launch the HelloWorld Activity, and have proper entries inside the journal each time you end this activity.
If you followed the tutorial, you might think: "Yeah, this doesn't seem that hard." Unfortunately, HelloWorld being the smallest application ever (here, consisting on one tiny, tiny little .py file), this of course was pretty quick and easy to do. Now for something like OOo4Kids, this will be much, much harder, for many reasons, and not only because of it's size.