Is there any difference between Ph.D, D.Sc, D.Litt and the similar degrees?
The meaning of these degrees vary by country. In some countries (especially in Europe), PhD is the "basic" degree. It's the one you get out of graduate school. D. Litt (aka. Doctor of Letters) and D.Sc (Doctor of Science) are the highest conferred degrees. You need sustained achievement at the top before these are awarded. Here's a quote from the Wikipedia article on D. Litt:
The Litt.D. degree is awarded to candidates whose record of published work and research shows conspicuous ability and originality and constitutes a distinguished and sustained achievement. University committee and board approval is required, and candidates must provide documented mastery of a particular area or field. The degree may also be awarded honoris causa to such individuals as the university or the learned body in question deems worthy of this highest academic award.
D.Sc is similar, except it's for the sciences as opposed to social sciences. Again, see the Wikipedia article, except there're many non-European countries who take D.Sc to be effectively equivalent to PhD.
Speaking literally, nothing at all except an indication of the field. However, life isn't quite that simple. Doctorates in general are intended to be research degrees. Research in Literature, or Mathematics, or whatever. The actual choice of designation is up to a granting institution and/or some governmental authority.
A person with a doctorate is expected to have the skills to extend the known state of a field in meaningful ways. Moreover, he or she is expected to have demonstrated that skill via an accepted dissertation and some period of study. The study includes both the breadth of the field and particular depth in some (usually small) aspect of it. A Master's degree doesn't have the same expectations and normally, philosophically, a person with this degree should be able to carry on the normal work of the field and to move with the field as it changes. It normally stresses breadth more than depth in a subfield (though there are exceptions).
However, not all doctorates are created equal and not all are, in fact, accepted as Research Degrees. This may be especially important to a candidate for a degree, especially one contemplating an academic career.
The UK and other countries that follow UK traditions also have the concept of a "Higher Doctorate." for a discussion of that concept, see the answer of Allure here.
The NSF in the US keeps a list of "Research Doctorates" that it considers "equivalent" to the PhD. This has an impact on getting grants, especially from the NSF and may have an effect on tenure decisions.
Wikipedia gives some of the distinctions and local variations.
I also discussed the US position of the NSF as an answer to another question here: https://academia.stackexchange.com/a/112004/75368
Normally you would also name the field if you earn a more "general sounding" degree such as PhD, than a more specific one such as D. Litt.