1、be good at (doing) sth.擅长于 =do well in，后接技能、学科

I am good at English， but Mary is good at maths.

我擅长英语,但是玛丽擅长数学。

2、be good for ...对……有益 与be bad for..(对......有害）是一对反义词

be good for health 有益于健康

Eating more vegetables is good for your health. 蔬菜对你的健康有好处。

Smokingis bad for your health. 吸烟对你的健康有害处。

3、be good with 对……有办法，善于应付……后接人或具体的事物,相当于get along with

Mary is good with old people. 玛丽和老人们相处的很好。

The new teacher is good with the children.新来的老师能和孩子们打成一片。

4、be good to 对…友好/有好处 =be friendly to

My dad always says that we should be good to others.

我爸爸总是说我们应该对别人友好。