Word stress means emphasizing or pronouncing some syllables in a word longer in time / higher in pitch and louder in sound than the other syllables in a word. We are talking about which syllables in a word «to stress».
Why do we need to understand stress?
Even if you correctly pronounce a word, it may not be understood by a native speaker because the stress is on the wrong part. So you need to understand where the stress is placed.
So stressed syllables are pronounced;
Unstressed syllables are pronounced;