Nowadays, there are many constructed languages which may serve for different functions. Some of these languages, like Esperanto, try to create an universal language for all people, while others have entertainment purposes. For example, we have the different languages that were created for a book series, such as the ones in The Lord of The Rings by Tolkien. Now, I'm going to speak about High Valyrian, which appears in A Song of Ice and Fire Series by George. R.R. Martin, also known as Games of Thrones.
In the books and TV series, High Valyrian was the language of Valyria and the Valyrian Freehold. It is no longer widely spoken due to the Doom of Valyria, although there are songs and books still sung and read in it. In Westeros, highborn children, specifically the Targaryens, they are taught Valyrian as a sign of their noble education. Corrupted dialects known as bastard Valyrian are spoken in the Free Cities and Slaver's Bay.
It wasn't actually created by George R.R. Martin, the author of the book, but by David J. Peterson. On the books, very few words are actually written in High Valyrian, but most of the time it is mentioned that a person is speaking a Valyrian Language. For the series, they wanted the actors to speak in High Valyrian those lines, so they decided to hire someone to build the language. The chosen one was David J. Peterson.
Peterson began working with the few words that George had published on the books, the most important ones being "Valar morghulis" and "Valar dohaeris." Peterson used these two phrases, which mean "All men must die" and "all men must serve" to create the whole conjugation of the new language. There are four grammatical numbers in the sistem: singular, plural, paucal and collective. For example, with the word "Man", the nouns are "vala" (man), "vali" (men), "valun" (some men), and "valar" (all men). There are also 4 grammatical genders, but they have nothing to do with biological gender. They are lunar, solar, terrestrial and aquatic.
This is a clip of Daenerys Tragaryen speaking High Valyrian in the TV Series, on the 4th episode of the 3 season. Here is what she says in High Valyrian, you can see the English translation on the subtitles.
Still, this isn't how it is actualy written in Valyrian. The creator of the Language, Peterson, decided that it was not worth it building the writing system yet, since it was barely used in the series. He says that he is looking forward building a writing system similar to hieroglyphics, even though at one point in the series a woman appears writing it in Latin Alfabet. Peterson mentions it is unfortunate that George R.R. Martin chose the word "dracarys" for dragonfire, because it is based on "draco", the latin word for dragon. Still, George R.R. Martin isn't really interested on the language. When compared to the Elvish language Tolkien constructed for LOTR, George says:
"Tolkien was a philologist, and an Oxford don, and could spend decades laboriously inventing Elvish in all its detail. I, alas, am only a hardworking SF and fantasy novel, and I don't have his gift for languages. That is to say, I have not actually created a Valyrian language. The best I could do was try to sketch in each of the chief tongues of my imaginary world in broad strokes, and give them each their characteristic sounds and spellings."