to do 就是不定式,接在某些动词后面的,七八年级的不定式一般表示 目的
ask sb to do sth 要某人(去)做某事
allow sb to do sth 允许某人(去)做某事
make sb to do sth 要某人(去)做某事
help sb to do sth 帮助某人 做某事
encourage sb to do sth 鼓励某人做某事
teach sb to do sth 教某人做某事
want sb to do 希望某人做某事
sb to do sth为不定式的复合结构,做宾语 如advise sb to do sth
eg. Our teachers often tell us to study hard.
He asks me to have a rest.
都可以做句子了....