You have to remember the pronunciation of each letter or combination of letters. Once you know how to pronounce a vowel or a consonant you always pronounce it the same way. The accent is always on the second syllable from the end ot the word.
Some Polish letters have diacritical marks.
These marks are meaningful in terms of pronunciation and cannot be omitted. C as the English 'ts' in cats. G as the English 'g' in girl. H as the Scottish or German 'ch' in loch. J as the English 'y' in yet.