一、so用作连词，主要用于表结果，意为“所以”：
It’s very cold, so wear a heavy coat. 外边很冷，因此穿一件厚大衣。
The door was locked, so we couldn’t get in. 门上锁了，所以我们进不去。
I couldn’t have won, so I didn’t go in for the race. 我不可能获胜，因此我没参赛。
The play began at eight, so they must dine at seven. 戏八点开始，因此他们必须七点吃饭。
It was dark, so I couldn’t see what was happening. 天很黑，所以我看不见发生了什么事。
There happened to be a policeman on the corner, so I asked him the way. 恰好拐角处有一位警察，我就向他问路了。
二、有时可与并列连词and连用，构成习语and so(相当so)：
He told me to do it and so I did it. 他叫我那么做，所以我就做了。
He worked hard and so he succeeded. 他勤奋工作，所以他取得了成功。
There was so much to eat and so few people to eat it. 有这么多东西可吃，而吃的人又这么少。
I forgot to post the letter, and so she never heard about my divorce. 我忘了寄那封信了，所以她一直不知道我离婚的事。
三、不要按汉语意思将“因为…所以…”直译为because…so…：
误：Because he was ill, so he couldn't come.(去掉because或so中任意一个)