NOD = Notice of Default
NTS = Notice of Trustee Sale
NFS = Notice of Foreclosure Sale
Not sure about LIT; probably something with liens?
Anyway, this seems to be about buying properties from Sheriff sales, or trying to pre-emptively contact people late on their mortgage to try to buy their house (at a deep discount, of course). Infomercial / hotel "real estate investing seminar" stuff.
It's difficult to purchase homes this way, and I believe it requires a certain level of aggressive personality (not to mention cash) to pursue it successfully. You really have to know what you're doing! There are many pitfalls, and you're competing against a small set of people who do it for a living.
If you're just starting out investing, it's an order of magnitude safer to buy properties listed by a broker (even REO/foreclosures). By the time properties are listed, liens have been extinguished, title is insurable, you're able to inspect, etc. Your risk is not much greater than buying a non-REO or foreclosure. If you have time and rehab skills, or the cash to purchase turnkey properties, it's possible to do quite well.