Formation of Names in Sindarin and Quenya

I've been having trouble creating names in Sindarin and Quenya. I wanted to come up with an original name for a character in my story, but I realized that my knowledge wasn't sufficient. I've studied various reference books and dictionaries, but I still haven't understood why names sometimes differ so much from their original meanings. Can anyone provide a detailed explanation of name formation? Sorry for being tongue-tied. I don't know English very well.

I don't know what you mean by "names sometimes differ so much from their original meanings". Can you give examples?

In Sindarin, a Celtic-like language, mutation-like phenomena of course play an important part in the combination of words into compounds. As far as I know, David Salo's description about the changes in element-initial and element-final consonants and the shortening of the vowels (and consonant clusters) in the elements of compounds is still valid to this day — it can be found in his book "A Gateway to Sindarin", on pages 178 - 190. Online pages that at least somewhat show these phenomena are:

"Compound Sindarin Names" at tolkiendil.com

"Sindarin Names" at Eldamo