Hi David
you probably sorted the concept out by now
however if not...
Each group or component has its own origin axis, usually left bottom side. If you right click on the axis you can change its position, but at this point, probably best to leave it.
if you double click to open a group/component within a group/component you will likely notice a shape defined axis and a dull smaller axis. This gives an idea of the relationship between the two objects.
The formulas and process is similar to a spreadsheet application, you can click the cells in to build the relationships rafter than typing
I find it convenient to build an object with known size and positions then figure first the lengths and then the positions
Philip
toggle to view formula
each object has own axis which is positioned in relationship to its container