ok... here goes
those settings are just a range of how many ohms you are testing for... so, while you should be able to test it at 200 (because a good ground should only have 0.xx ohms) a bad ground can sometimes give you kilo or even mega ohm readings (and remember here, the higher ohm reading you get, that means the more resistance you will have for current flow) .... so, to start out i would put the range right in the middle, and then adjust from there... (so say you have it ranged at 20k, and you get a reading of .0002 or something like that, take it to a lower range like 2k or 200).
now, for where your going to want to test it and how....
what your DMM is doing when testing ohms, is sending a very small current from the positive prod, through whatever you're testing, and then back into the negative prod, so that it can measure the resistance... just keep that in mind.
so to test your ground, find a chassis ground a lil away from the ground you'll be testing (a bolt into the chassis will work, as long as it's steel, and unpainted)
that is where you will have your negative prod.
then take your positive prod, and place it on the lug that you have for your ground (make sure not to touch the bolt that is holding it in, as this can cause a false reading) ... when you do this, you should get 0.xx on your 200 setting (meaning you have 0.xx ohm resistance between the lug and chassis)... if you get 20k ohms or some high number like that, the ground is bad... if you get a good reading, then test that same ground, from the end of the actual wire to the chassis (the bolt i was talking about earlier)... and so on... do this for all your grounds, so that you can eliminate each ground as being good or bad.
hope that all makes sense