The corals we keep in our tanks, plus some of their relatives such as sea anemones, jellyfish, hydrozoans, etc all belong to the PHYLUM CNIDARIA (pronounced with a silent C). <When I was just a kid 30+ years ago, this used to be called PHYLUM COELENTERATA.>
One common denominator among all Cnidarians is that they possess stinging cells (very strong in some Cnidarians such as jellyfish, but very weak in some other Cnidarians such as most softies).
Cnidarian bodies may have one of two general types. The first body type is that of a sessile (fixed and non-moving) polyp(s) <such as in a coral or sea anemone>. The second body type is that of a motile (free-swimming) medusa <such as a jellyfish>.
Within PHYLUM CNIDARIA, there are three classes:
1.1 Class Hydrozoa - the "stinging" hydroids and sea ferns. Also includes the stinging Millepora (commonly called fire corals, although they are not corals). The Hydrozoan body type is that of a medusa when young, but becoming polyps when old (or sometimes, alternating their body types with every generation!).
1.2 Class Scyphozoa - the over 200 types of jellyfish. Their body type is always that of a medusa.
1.3 Class Anthozoa - the corals and their relatives. Their body type is always that of a polyp.
The "corals" and related livestock that we usually keep all belong to Class Anthozoa. Within Class Anthozoa, there are several further <non-extinct> subdivisions or "Orders". These are:
1.3.1 Order Alcyonacea - the soft corals, such as leather, colt, and tree corals
1.3.2 Order Gorgonacea - sea fans, sea whips, gorgonians, etc
1.3.3 Order Helioporacea (formerly Coenothecalia) - only one representative: the easy-to-keep "blue coral" or Heliopora <Mang Jun now often sells this, after he learned how to ID and care for it>
1.3.4 Order Pennatulacea - sea pens
1.3.5 Order Stolonifera - only one genus: Tubipora or Pipe Organ Corals (you don't care to know what makes this unique).
1.3.6 Order Telastacea - certain rare corals: you don't want to know, because I don't know either
<<The above six orders are collectively called Subclass Alcyonaria or Octocorallia. Somehow, their tentacles and/or mesentaries have some form of 8-way symmetry>>
1.3.7 Order Actinaria - sea anemones
1.3.8 Order Antipatharia - black corals (we never see this in cartimar, only found in deep water up to 300 feet)
1.3.9 Order Ceriantharia - tube anemones
1.3.10 Order Corallimorphia - corallimorphs or "mushrooms" or "false corals" or "colonial anemones" (best examples are Actinodiscus and Ricordea)
1.3.11 Order Scleractinia - stony or hard corals (LPS and SPS)
1.3.12 Order Zoanthidea - commonly called zoos or zoanthids (such as Zoanthus, Palythoa, Protopalythoa, etc)
<< The above six orders are collectively called Subclass Zoantharia or Hexacorallia, because they exhibit a six-way symmetry in their tentacles, etc>>
Other than 1.3.6 Order Telastacea and 1.3.8 Order Antipatharia, you can see livestock from all the above orders of Class Anthozoa being sold in Cartimar at one time or another.
So, a "soft coral" is technically really limited to 1.3.1 Order Alcyonacea. This will include all the common softies we know, including Sarcophyton, Sinularia, Xenia, Anthelia, Litophyton, Stereonephthya, Lobophyton, Cladiella, Capnella, Clavularia, Pachyclavularia, etc
But as mentioned elsewhere, when people in ReefPhilippines talk of softies, they often include sea fans, zoanthids, and corallimorphs. I guess its because most of these livestock all share a certain "easiness" to care for.
By understanding the taxonomy of the "soft corals", I guess one could infer common aquarium issues across certain related livestock, such as in terms of husbandry. This would also be a good start if one wanted to go deeper into the marine biology aspect of our hobby.
In closing, I strongly request all newbies to start off their reef tanks with soft corals only, and only after a few years of FOWLR experience. The chance of success (and feeling of accomplishment) will be much higher. These livestock are much easier to care for, as they will tolerate newbie mistakes, such as imperfect water parameters and deviations in salinity, temperature and flow. Don't get me wrong: there are some very difficult (even impossible) soft corals, but many are quite easy to care for.
Equally important, most softies are not scarce resources in the reef that could conceivably become extinct. They are an easily sustainable reef resource. (In fact, I think we can work with completely tank-grown and fragged softies). Thus, this will not be a lightning rod for complaints against our hobby.
After a year or so of managing a softie tank, then one will presumably already understand a few things:
1) the basic ethics of our hobby, especially recognizing our obligations to keep our livestock alive and to protect our reef resources
2) the basic scientific principles (chemistry, marine biology, physics, etc) that make our tanks work, including the equipment therein
3) the basic husbandry skills for aquariums, including familiarity with and affinity to our livestock
4) ancillary aquarium skills such as plumbing, electricals, photography, etc
5) the humility to accept that we really know very little (in spite of all our posts in RP
), and we still have so much more to learn about the hobby (it's an endless journey...) 
At that point, and only at that point, should one then consider going into more sophisticated reef tanks (such as mixed reefs, LPS only, SPS only, special biotopes, etc).
HTH,
Phil
