pronouncation

pronouncation
Your question isn't very clear, but the general answer (if you are referring to English in particular) is that English comes from many sources, and that fact has influenced pronounciation, so that words may sound the same but be spelled differently. This means, for example, that a word that comes from an early Germanic source may use a different combination of letters to produce the same sound as a word from an Old French source.

Many English words derive originally from Greek, many others from Latin, and the spelling and/or pronounciation of the modern English word will be affected accordingly. A word from Greek will use the combination "ch" to make the sound that is represented by "k" in the English alphabet. So the example you give, "psychology", clues you in to the fact that the source was a Greek word.

thank you
thank you