Firstly its metres, even in American because it's is an international unit, you can't change it even if you don't know how to use it. A meter is something that measures something, like a water meter.
Secondly, 200 sq metres, means 200 x one metre squares, NOT 200 x 200 m.
20sq metres would be a square roughly 14 metres on each side , say 50 ft., or a 200 m long strip 1m wide, the area covered by Usian Bolt (and everyone else) in the 200m race.
A tennis court is 260 sq m (roughly 24 x 11), so slightly less than a tennis court is the easiest way to visualise it.