Dictionary forms + と…    whenever…；if… (Refer to the grammar dictionary "To" pp.480 – 482 for more sample sentences.)

とmarks a conditional clause and indicates:

1. a logical cause –effect relationship (non-controllable).  E.g.  春になるとあたたかくなります。　Spring has come (it becomes spring) (and what is naturally following is), it becomes warm.
2. an action or event and its inevitable (or natural or habitual) consequence.  The main clause expresses something happens, not something the speaker of the hearer intentionally does.  Therefore, it cannot be used with such endings as –mashoo, te-kudasai, and –tai desu (those which indicate a command, a request, a suggestion, an invitation or a volitional sentences.)

 

日本人は、お酒を飲むと、顔が赤くなります。When(ever) a Japanese drink sake (and what is  naturally following is), his/her face becomes red.

毎日日本語を練習すると、上手になります。If you study Japanse every day, you will be good at it.　

ごはんを食べると、眠たくなります。When we eat a meal, we becomes drawsy.

魚は古くなると、おいしくなくなります。If fish becomes old, it becomes not tasty.

春になると、桜がきれいにさいて、ハイキングに行きたくなります。When it becomes spring, the cherry trees blosson, and it makes me want to go to hiking.
冬になると、雪が積もって、スキーやスケートをやりたくなります。When it becomes winter, snow falls, and it makes me want to go skiing and skating.