besides 意为：“除...之外（还有）.”有附加含义.与in addition to 同义.
except 意为：“除...以外（没了）.”有排除的含义.
except for 意为：“除...之外,其他都...”用来评价事物的美中不足.
but 意为：除了.语气强烈.
如：
She knows two other foriegn languages besides English.
她除了英语外还知道两种其他外语.
He goes to school every day except Sunday.
他除了周日每天都去学校.
Your composition is good except for a few spelling mistakes.
你的作品除了有些拼写错误外都很好.
I really want to tell you the truth,but I can't.
我真的很想告诉你事实,可是我不能.