While Tolkien is attributed with writing several languages as part of developing his fictional worlds, the Elvish languages developed for his stories includes basic terminology and are not a languages with large or complex vocabularies.
It's not entirely guaranteed that you'll learn to write your name in Elvish in ten minutes, but one thing that you're guaranteed to find at this website is a much better understanding of the alphabet and how the language works.
These two languages are the most developed of the Lord of the Rings Elvish languages because material left behind by Tolkien on these two languages is substantial compared to the other Elvish languages found in his writings.
With the resources listed above, you should have no problem learning not only the basic Elvish alphabet, but also how to write entire sentences and even pages of text in the Tengwar language.
Along with dictionary help, they provide Sindarin Elvish language tools including a summary of Sindarin grammar and Sindarin pronouns as well as courses for the two primary Elvish languages.
Fauskanger has taken great care to include links to various sites that can give you more details and information about all things elvish, including names and the elvish language of Arda.
One phenomenon that has increased over the past years and seems directly related to the LOTR movies is that people are naming their babies with elvish names, especially those from LOTR.
Another consideration when looking for a dictionary is to be sure the dictionary you use online or buy in print is based on Lord of the Rings Elvish and not some other Elvish language.
For those who role play and want to select an elvish name, the common rule in creating an elf name is to use an adjective and noun combination as given in the example of Legolas.
According to Tolkien's linguistic dictionary, The Lhamas, if you examine the elvish names, you'll notice that most of them are compound words or in many instances form a phrase.