Generally Latin letters are pronounced the same as their English counterparts, but there are a few key exceptions.
C & G. C as in Caesar. However, nowadays we often pronounce Caesar as if it were spelled Seezer. In fact, in Latin C is always hard, never soft. In other words, it is always pronounced like a K, and never like an S. So Caesar is more like the German Kaiser, unsurprisingly.
G, as well, is always hard and never soft. So when we have the word lex (law), it's genitive form is legis, and rather than being pronounced like legislature (which is obviously derived from the Latin word), the G in legis is pronounced like the G in Vegas, as in Las Vegas.
C and G also were interchanged, the history is unclear to me (something about the Etruscan alphabet being borrowed, and not having the same sounds, but I don't care to explain any further), but it is the reason that sometimes we see the nomen (name) Caius, and sometimes we see Gaius, or like wise, sometimes we see Cnaeus, and sometimes we see Gnaeus. The names, though, when abbreviated, always use C rather than G. So, for example, Gaius Iulius Caesar would be C Iulius Caesar, or Gnaeus Pompeius Magnus (Pompey the Great) would be Cn Pompeius Magnus.
S is never pronounced like Z, that I can think of, but always like S.
The other big ones we need to get down are the vowels, including Y. Vowel sounds in Latin are funny, because unlike in English, there aren't really two different sounds they can make, long and short. The long sound for a Latin vowel is just literally pronouncing it for a longer period, and the short sound is doing it for a shorter period. For those of you familiar with pretty much any other language, the vowels are pronounced like other Romance language vowels, or even more broadly, other Indo-European vowels, not like English vowels. English vowels got screwed up during the English vowel shift.
A. A sounds like the word "uh". It doesn't make the sound which we call it, sort of a "hey" without the H. It always sounds like what we would term a short A sound, never long. It never sounds like the English A does in the word "cat". It sounds like the A in the word "art" or either the first or last A in "Arabia", but not the middle A in the way we tend to pronounce Arabia.
E. E sounds like the English long A. It does not sound like the English long E, or "eee", rather, it sounds like the end of the word "sorbet". This is the long E sound in Latin. The short E sound is literally just a shortened version of the sound, so it sounds like "eh" as in our commonly used words on teh blogs: "teh", or "meh".
I. I sounds like the English long E, so it sonds like "eee" as in the words "chic" or when Arnold Schwarzenegger says "California". The short I sounds like the I in the word "it". In front of another vowel, I will sound like an English Y. For example, iacio would be pronounced like eeyahkeeyo. This is beginning to see the I used as a consonant, and lays the foundation for the eventual creation of the letter J.
U. In a name like Iulius, the first U sounds like the very name of the letter U, while the second sounds like the common utterance "uh". When a U is placed in front of a vowel, it creates a double-U-ish sound, which I'll explain more about later. Just think of a word like the name Stuart, and the alternate spelling Stewart, and you can see the basics of how that works.
Y. Y, in Latin, usually sounds like a short I or U in English. For example, the Y in tryst.
Lastly, H. In Latin, H only adds a "breathy" sound to a word. One rarely sees it, and often no pronunciation is necessary, and if any is necessary, then it is only very little. For example, often I will find an H in a word that we would not normally use it with, like for the Adriatic Sea I will see "Hadriatic", and I basically just exhale audibly as I begin to pronounce the word, and that's how I pronounce the H. Often H appears in foreign words, like Athens (Athenae), but that's starting to get into the next topic, letter combinations and diphthongs (ph, th, ch, rh, ae, oe, i+vowel, u+vowel).
Previous lessons:
I