Cruiser.X, Cruiser.Y refers to whatever cruiser has been 'picked' through condition. For example:
+ Cruiser.X > 100
-> Spawn Asteroid at Cruiser.X, Cruiser.Y
In this example, the Cruiser.X > 100 condition picks all cruisers with X greater than 100. That's what 'picking' is like, it is rather intuitive - it is basically filtering, so actions are executed on the objects you want
If there is no condition or such, all instances of the Cruiser will be picked by default.