Having some difficulties with the Latin language. I have need of two phrases, terms or names. Any help would be much appreciated!

A name of a place (noun): "Castle of Life and Death" How to say this in Latin as a name of a place?

Closest I can come to is: "Castellum of Vita and Letum" or "Moenia of Vita quod Nex"

The next is an entity "Most Beloved One" as a reference to one person.

"carus Unus" ?

Also it would be a huge help to me to know how to use words such as (and, the, of, as,) etc., *prepositions* in the Latin language in simple sentences. I mean what are they and are they used differently from other languages? If I recall correctly I was told that the English language uses too many unnecessary words which seems about right so I am having difficulty knowing when words above would be used or not used.

Thanks in advance and forgive me if my question is confusing.