How do you know when to put an accent or a stress on a word?

Normally in Latin languages, a word will have a stress on its penultimate vowel. However, if you say the word to yourself and hear that the stress is not on the penultimate vowel but indeed on the last letter, then an accent must be placed. Now understanding what accent ot use is important, most of the time the accent will be acute (é) yet on the commonly used verb 'to be'- (essere) the accent on the first person singular will be grave (è). Unfortunately only memory and practice let you remember on particular words.