I want to tell you how can keep healthy.为什么是病句

可以改成
I want to tell you how I can keep healthy。这个就成为一个从句了。＼

或者改成 I want to tell you how to keep healthy．
这样就是一个简单句

I want to tell you how to keep healthy
你写的句子是典型的中国式英语。怎样能保持健康，正确的用法是how to keep

"how can keep healthy"在这里作宾补，要么是从句，要么是短语，从句应改为"how I can keep healthy"，短语应改为" how to keep healthy"

i will tell u how to keep healthy .