WHOA, DANGER, WILL ROBINSON!!!!!!!!!!!!!!!!!!
First, don't buy on store recommendations. If you get a stony coral you are committing to calcium supplementation for the life of your tank. If you get a softie, you have to take care about it over-multiplying. And both require a separate strength of light, which, yes, you can get by setting some atop, some at bottom of rock, but how far? And all should start on the bottom and move upward, unless you know the coral.
Gluing to structural rock may mean taking your tank apart if you end up with the coral that ate Chicago. Some grow wildly. Right now I'm coping with a one tiny scrap of xenia that got into my lps reef, started out as a smidge of one on a rock, and now is a palm-sized mass. I'm told they hate euphyllias, which is what I specialize in, and I hope this is true.
You MUST DIP YOUR CORALS or you risk the coral equivalent of ich that can be as bad to get rid of. This is not 'freshwater dip'. This is a special preparation like CoralRX, which must be mixed in a bucket and a bucket reserved only for that purpose.
Softie coral, particularly zoas, should be held in observation for a few days to make sure predator eggs that survive the dip do not hatch a new batch. If this happens, re-dip.
If the coral you buy was kept on the same sump system as fish in the store, you do have a small risk of actual ich coming in encrusted on the plug---small risk, but 100% if you happen to get it. A 72 day quarantine may be indicated. And it is entirely reasonable to flat-out ask a store, face-to-face, or online, whether that is the case. Doesn't necessarily affect your purchase, except in telling you this coral may need a 72 day qt and of course some lights that will keep it alive for 72 days.
Most of all do not rush down to the lfs in a must-buy mood, with no consideration of the strength of your lights (highly specialized very bright lights for sps ---10,000 to 13000 k, metal halide or T5 or highest-end LEDs, top of the rocks, and prone to exotic hard to see pests...with a skimmer that keeps the water absolutely crystal clear as drinking water.
LPS is top to middle of the rocks, even bottom for plate and slipper and bubble...with 10000 to 13000 k, but moderate skimming.
softies are T5 and dimmer, suck their food from the water, so over-skimming not good with them.
Mostly, friends, heads-up---do not rush blindly into this, or you will kill coral and waste your money and infest your tank with nudibranchs and red bug. Coral dip, follow instructions, observe your zoas or any rock kept with them, and do not buy anything you do not know the name and type of. If you are not equipped for sps do not buy sps. If you do not have the light for lps, save your money. If you are going softie, also buy some carbon, because they pitch fits and carbon helps take their spit out of the water.
Space your corals far apart. Some lps (bubble, galaxia, brain, and others) develop tentacles (sweepers) when feeding that can reach 6".
Remember that light itself is food for corals---like plants: sps lives almost entirely on it; lps half what it sucks from the water and half from light; and softies maybe a quarter of what they eat is light, the rest from the water.
Remember that all stony coral sucks calcium out of the water continually. If you have stony you must keep this reading at 420 by dosing or by kalk in the topoff or by a calcium reactor (really big reefs.)
Remember that the wrong light can starve a coral or burn it fatally.
Remember that much of that fine print in your reef salt mix is coral food.
