Simple, once you've done it the first time. You need to set a trigger at a suitable location, eg., at a drop or load point for example. Then in "Edit Session" where you place the "Rules" you need to add "Ordered List". Then add "Trigger Check" which must be indented (once) to the right. Edit this to add the trigger number, usually have it trigger by whichever loco you are using (otherwise anything could trigger it). Then below that (don't indent further) you may want to add a popup message about what has happened or reason for score (eg, "That's the first load dropped"). Then below that add "Variable Modify" and set that to give whatever points you need.
Presumably you've already added (first) "Ranked Session Begin".
A better way to learn is look at an existing, simple session, and see how they do it.
