The language of Sindarin is the tongue spoken throughout Beleriand in the first age and later on through history in Middle-earth as we know it from The Lord of the Rings. The reason that Sindarin is the main language is mainly due to the seperation of the elves during the summoning to Valinor.
The elves split up into several groups while travelling. Some went to Valinor, some stayed behind. Over the years, the language of the elves that stayed behind evolved differently than to that of the elves that went to Valinor. The language they called Sindarin.
When a group of Elves returned from Valinor, they met up with the elves that had stayed behind and realized how much their tongues now varied. The current king of the large realm of Doriath, Thingol, eventually insisted that they speak Sindarin while they were in his realm. Elves being very adaptive, picked it up in no time, reserving their own tongue, Quenya, for more traditional and formal occasions.
Continuing on into the third age during the time of Lord of the Rings, Sindarin was still the main tongue of the elves in Middle-Earth. Basically, if you fell into Middle-earth and Eru forbid, bump into Legolas (or an elf of your choice), this is the language you would use to greet him(/her).
Sindarin is the Tolkien language with the most resources available for studying. I can’t say that it’s the easiest language to learn but I didn’t find it overly difficult.
As with every language, grammar is an important key. Infact, I wouldn’t recommend speaking without it. The wisest place to start when learning Sindarin is indeed with the grammar. Don’t get me wrong, vocabularly is also extremely important. Considering without it, you can’t communicate.
Most websites that I’ve seen that give one information and lessons tend to carry the same basic content. So in the end, it’s up to you where you choose to study. Personally, I use a mix of them.
Council of Elrond offers workbooks, forum assitance, dictionary and encyclopedias. This is my main resource for learning Sindarin.
Ardalambion is also a very good site. I’ve known more people to learn from here. I occasionally use it but unfortunately, I find the layout confusing.
I’ve been studying Sindarin for several years now. I’m also very good with Sindarin tengwar, the form of script used. If you need any extra guidance outside of the information provided, feel free to post questions in the thread or you can also pm me
here. I’m willing to do translations in both script and general Sindarin. If you’d like a translation, again, let me know.
**This is the best Sindarin dictionary one can lay their hands on. It’s a free download to your computer where you will have it at your fingertips. It also does tengwar in Sindarin, Quenya, Black Speech and English.