Heya Winggeek,
The circle to land does catch people out at first as its not done in the sim, but after one of them you should get the hang of it fairly lively!!
A circle to land is a circle to land. You don't begin on the ground. In your ME IR Flight Test (chances are) it will be your last approach. So for example, MDA is 400ft and ACA is 300ft.
You arrive at 450ft and the examiner takes down the screens, allowing you to descend further to ACA. As you approach ACA he/she calls go around.
As the simulated cloud (the screens) were taken away at 450ft, you have a situation where you have a simulated low cloud base. Although for the circle to land you will be let climb to an altitude of 600ft AGL (depending on the aerodrome and time of day).
So it is basicly a go around but in a situation where you want to land ASAP. So instead you just 'buzz off round the circuit' at 600ft for another go (and to show the examine you can indeed do it).
Great fun, enjoy it!!