Strictly speaking there are no sounds of letters, because letters do not speak.
We commonly use the term, the sounds of letters, to refer to letters and their related sounds because we are literate, and for literate people the written form of language is usually the most important.
Reading and writing, on the other hand, are not skills for which we have built-in abilities. They are not things we can learn purely by being exposed to them. Instead, this knowledge and these skills have to be specifically taught. Having literate people around them does not help small children learn to read; it might instil in them a great desire to read, and it might help them gain some understanding of the principles underlying reading and writing (e.g. we start on this side of the page, and work our way over to the other side of the page) – but it doesn’t help them “pick up” the specifics of letters, their related sounds, and handwriting.
Learning to read is much easier in some languages than others. In a few languages there is a very close correlation between a sound and the way that sound is represented in writing. This is especially true when only one letter or sign is ever used to represent that sound.
In reality, though, the oral form of language is more important for three reasons: it came first in history, the oral form comes first in each person’s development, and the written English language is based on its oral form.
Oral language is part of everyone’s natural development. Children, even if they’re deaf, babble as babies. When children hear people speak, they naturally learn the sounds in that language. If the speakers they hear speak more than one tongue, small children naturally pick up each of those languages, and quite early on, they even manage to distinguish between the different languages.
This is not true of English. In our modern English vocabulary, we use words made up of sounds from many different languages. Words from Latin form 29% of our vocabulary; words from French also make up 29% of our vocabulary; words from German, 26%; words from Greek, 6%; and words from other languages (including Anglo-Saxon) form the remaining 10%.
What has added to the confusion is that often, when a word from another language was introduced into English, the English version of the word used the same spelling as the word in the original language. This has resulted in our having alternative ways to spell the same sound.
In order for readers to be able to read fluently, they need to know these alternative spellings. Many learn to read courses only teach the sounds of the Alphabet Letters. Some courses teach some of the sounds of the other letters (e.g. th and sh). Only the comprehensive courses teach both the Alphabet and Other sounds.
The course offered on this site is one of the comprehensive type learn to read courses; if you’d like to learn more about it, go to the Articles page, and read the Article – Course – About this Course, or click Reading Course, in the menu.