All letters used in Lojban, including the apparent punctuation marks, have sounds assigned to them. In the cases where two vowels are placed side by side, they form a diphthong – a blending of the two vowel sounds into a single combined sound. In the cases of some consonant combinations, the pronouncing of the two letters together produces a sound that might sound like it should be a single letter rather than two letters (e.g. <tc> creates the same sound as the combination "ch" would in English), but in these cases this results from that actual blending of the two letters' unique sounds.
In Lojban a letter does not have more than one sound, and no two letters make the same sound. In Lojban the letter C always makes the sound that in English is normally spelled "sh", while the letter S always makes the sound normally associated with that letter in English, and the letter K always makes the so-called 'hard C' sound.
Because every letter in Lojban has a unique sound, spelling and reading are dramatically easier than they would be in another language. Words have only one possible pronunciation, and there are no silent letters to catch the unwary.