The role of stress in Russian words

It is very important to make the right stress in Russian words not only because in this way the words will sound right and good, but also because the meaning of word can depend on stress.
I will give an example of some words which have the same writing but different meaning because of the stress:

зАмок - замОк
                             зАмок - it is a castle
                             замОк - it is a lock

хлОпок - хлопОк
                             хлОпок - it is a cotton
                             хлопОк - it is a swat

мУка - мукА
                            мУка - it is anguish, throe
                            мукА - it is a flour

Атлас - атлАс
                            Атлас - it is atlas
                            атлАс - it is a satin

бЕлки - белкИ
                            бЕлки - it is plural of squirell
                            белкИ - it is proteins

плАчу - плачУ
                            плАчу - it means the verb "to cry" in first person singular
                                          (like "I'm crying" - "Я плАчу")
                            плачУ -  it means the verb "to pay" in first person singular
                                          (like "I pay money" - "Я плачУ деньги")

There are not too many the same words with different stress in Russian, but you should remember the main of them, it helps you to understand the oral speech right in some cases.

зАмок - замОк