It is very important to have correct pronunciation. You can learn a lot of words and grammar rules, but if you don’t pronounce the words correctly nobody will be able to understand what is it that you are trying to say. That is why it is so important to pronounce Russian words and expressions in a clear correct way, and try to imitate the way native speakers talk as much as you can.
One of the most common mistakes students make is the wrong stress. This mistake can change the meaning of the word completely, or just make it unintelligible to your speaking partners’ ears.
“Stress” means that one of the syllables in a word is pronounced with additional strength. In some languages the stress is fixed on a certain syllable, for example, on the last one. In Russian, stress placement is mobile. It means that any syllable in a word can be stressed. It is impossible to guess which syllable exactly the stress will be on. Stressed syllables are only underlined in books for beginner and low-level learners. So, when you come across a new word, you should consult a dictionary.
Stressed and unstressed vowels are pronounced differently. Unstressed vowels undergo become shorter and change their sound slightly.
“O” in an unstressed syllable which comes before the stressed vowel or at the end of the word is pronounced as a sound which is similar to a short [а].
Compare (the stressed syllable is underlined):
он – она
моль – плохо
In other syllables the unstressed vowel “o” is pronounced very shortly. It resembles something similar to an [а] and an [э] at the same time.
“Е” in an unstressed syllable is pronounced as something similar to both [е] и [и]. It is written phonetically as [ие].
The vowel “я” in an unstressed position will be pronounced in the same way.
The other vowels: у, ю, и, ы in an unstressed position are pronounced as shorter sounds than they would be pronounced when they’re in a stressed syllable.
Makovetskaja R., Truscina L. Il Russo. Corso elementare.