跟中文的区别的,中文的逗号可以隔开两个独立的句子,如：今天天气很好,我会出去.
但是英文这么说：It's a nice day today ,I will go out.就是错的.
应该说：It's a nice day today and I will go out.
英文逗号一般情况下不能用于连接两个独立分句,可以用来分割一个复合句,如：
The chairman rapped on the table,the audience quieted down.(误)
The chairman rapped on the table,and the audience quieted down.(正)