First of all, is there actually a user document on how the application works or do we have to ask everything here?

Other questions which have stumped me in the meantime.

1. In the Properties window what do the blue lines to the left of some of the controls mean?

2. In the Properties window for Heading how do I make the units 'em' and not 'px'?

Malc

Blue means the element has the property set to class.
Orange means the element has the property set to ID.
Magenta means the element has a property set to type.

Thanks Ross

To save me asking this sort of question time and time again, where could I find this information?

Secondly, how do I change font size to 'em' ? I have tried the obvious such as clicking on 'px' in the hope that a drop down appears but I am baffled.

Cheers
Malc

This should answer both of your questions.
The em vs px depends on the grid you select
http://www.coffeecup.com/responsive-layout-maker-pro/

Ah, brilliant. Thanks.