start to do sth .start doing sth.

I start to do my homework when the telephone rings. (还没有做作业）
We start to cook. （还没有做饭）
I start doing my homework when the telephone rings. （正在做作业）
We start doing cook. （正在做饭）

I start to do homework this afternoon.
I start to see this film at 4 o'clock this afternoon.
I start having breakfast at 6.30 in the morning.
Our school start having the first class at 7.30 in the morning.本回答被网友采纳

其实两个单词意思都是一样的。