Background
There are many different pronunciations of Latin. Currently the most common in English-speaking countries is the restored ancient pronunciation described below, which is a fairly close approximation of the way educated Romans of the late Republic pronounced Latin. Even in antiquity, however, there was some variation in pronunciation, and this variation greatly increased in the middle ages, when Latin was commonly pronounced like the pronouncer's native language. Remnants of the diverse pronunciations produced by this system can be found in what is now known as ecclesiastical or church Latin (which is effectively pronounced like Italian) and in Latin names that have become part of the English language (which are effectively pronounced like English). For example the name Cicerō is pronounced Kikero in the restored pronunciation, Cheechero in the ecclesiastical pronunciation, and Sisero in the English pronunciation. This diversity can lead to serious misunderstanding, because the various pronunciations are not easily mutually comprehensible, so when learning Latin it is important to master the pronunciation used by those who will be teaching you (normally the one described below), so that what you say will be understood correctly.
Consonants
In the restored pronunciation most consonants are pronounced in Latin like one of their pronunciations in English, but Latin consonants normally have only one sound regardless of what other letters appear nearby, whereas in English the same letter may have very different sounds in different words. The differences, therefore, can be considerable in practice. The most important of them are:
c is pronounced hard, like the c in ‘cold’, never soft like the c in ‘city’ (i.e. always like k, never like s).
g is pronounced hard, like the g in ‘get’, never soft like the g in ‘gem’ (i.e. never like j).
i is pronounced like the y in ‘yet’ when it is a consonant (i is usually a consonant when a word begins with i + vowel, and when i appears between two vowels).
qu is pronounced like the qu in ‘quick’, never like the qu in ‘unique’ (i.e. always like kw, never like k).