How to use the tenses?

Since there are quite a number of websites in which you can learn tenses, I would just list some of them which are simple and easy to understand.

- 英文文法基礎:
http://www.npc.edu.hk/staff/~ngtungying/english_grammar/
(This web is in Chinese and it covers not only tenses, but also other grammar tutorial)

- English Club
http://www.englishclub.com/grammar/verb-tenses.htm
(This site includes all the common tenses with tabels and examples)

- Englishpage
http://www.englishpage.com/index.html
(This web is useful as it provides explanation, examples and exercises)

- HK Education City
http://www.hkedcity.net/
(This site is for HK students and you can find many resources related to English and other subjects)

I hope these can help you!