floating exchange rate means that the value of our currency fluctuates - all other things being equal, when the $A appreciates, imports become relatively cheaper and exports become relatively more expensive overseas (less internationally competitive). since imports are cheaper, we import more...and since exports are more expensive overseas, we are able to export less...you can see here that our trade balance surplus decreases (or deficit increases) simply due to an appreciation in the $A (only made possible by a floating exchange rate). the opposite is true for a depreciation in the $A.
I hope this helps! goodluck!