This title makes this sound a difficult topic to revise, but it isn’t. firstly, global = over the whole world, then atmospheric = to do with the atmosphere and finally, circulation = moving around. In other words its how and why the atmosphere moves around the Earth. And once you know this you can then link it to the ecosystems topic, as global atmospheric circulation controls a lot of world climates which of course influence different BIOMES. (The two biomes we studied are: semi-arid and tropical rainforest.)
Firstly remember that
Rising air cools as it rises, so it cools, water vapour will cool, clouds will form and therefore three is a HIGHER CHANCE OF PRECIPITATION IN AREAS OF LOW PRESSURE (sometimes called depressions)
Descending air warms and therefore there is no condensation and LESS CHANCE OF PRECIPITATION IN HIGH PRESSURE AREAS (sometimes called anticyclones)
Since it is hotter at the equator, air rises here and creates area of low pressure. (So there is a lot of rainfall here. This is where you get tropical rainforests.) This risen air spreads out from the equator, cools and descends around 30 degrees north and south of the equator (area of less rainfall so deserts and semi-arid biomes here). This paragraph describes the movement of the Hadley cell which you can see in this diagram; it is labelled 1.
Additionally the rest of the global circulation is very well explained by this American teacher to his class. You need only watch up to 4:00 minutes.
Once you think you understand this global circulation, test yourself and use p. 75 from the revision guide to link global atmospheric circulation to biomes. If you need some more help with this you can read p. 210-11 in New Wider world.