Whether a syllable in a Latin word was stressed or not can generally be guessed at from the modern descendant or reflex of the word (assuming there is one), given that for the vast majority of words the locus of the stress has remained largely unchanged (although many words have been shortened due to natural sound change). For example, modern madera ‘wood’ is stressed on the [e] just like its etymon materia and hostal ‘bed and breakfast’ is stressed on the [a] just like its etymon hospitalem.
The basic rule of word stress in Latin was that words were normally stressed on the penultimate syllable unless that syllable was short (i.e. open with a short vowel as its nucleus), in which case the stress fell on the antepenultimate syllable. So, for example, the verb form audīmus ‘we hear’ was stressed on the penultimate syllable (due to the long ī), whereas audīvĭmus ‘we heard’ was stressed on the antepenultimate syllable (due to the short ĭ).