For a far, faaar more detailed explanation, go here: The Tolkienian Linguistics FAQ and Frequently Needed Answers
On the web you could try Thorsten Renk's Pedin Edhellin - a Sindarin Course, found under Resources and Secondary works (on the website Amarie gave). As long as one notes it is Neo-Sindarin and 'introductory'...
Thorsten offers the most up-to-date and accurate web-based account of Neo-Sindarin (that is, a synthetic and regularized form of Sindarin formed by the selective piecing-together of evidences from across decades of Tolkien's successive versions and elaborations of Noldorin and Sindarin) as a series of graded courses in a (gzipped) PDF file. Highly recommended as an introduction to more rigorous and detailed study of Tolkien's own Sindarin(s).' E. L. F.
There is also a 'new' Primary Source from Tolkien published in Parma Eldalamberon 17 which is very interesting and will also help illustrate that not everything Tolkien had published (never mind what he had never published) was 'safe' from the joy of creative revision (or 'niggling').