回答如下：

【一】不定式由以下2种情况

(1) 不定式to+行为动词原形(do)：

To learn a foreign language is not easy.

(2) 不定式to+系动词原形(be)

To be happy every day is very important for us.

【二】不定式+to do / 不定式 to be 区别

(1) to do 表示一种动作,是用来说明它的逻辑主语执行的动作行为（可以作除谓语之外任何其他成分）(to do 表示与其逻辑主语有一种逻辑上的主谓关系）

(2) to be 表示一种状态，是用来说明它的逻辑主语所处某种状态.

例如：（to be 表示与其逻辑主语由一种逻辑上的主系表关系）

A lot of people want to have a lot of money.(表示动作)

A lot of people want to be rich.（表示一种状态）

To be healthy every day is the most important. (表示动作)

To have good health every is the most important（表示一种状态）

To be famous is her goal.=Her goal is to be famous. （表示一种状态）

To get much wealth is her goal=her goal is to get much money(表示动作)

【三】有些动词可以用不定式+to do作宾语补足语，有些动词只能用不定式to be作宾语补足语

The doctor advised her not to eat too much sugar.

I wish you to go to the meeting with me.

I persuaded him to give up smoking.

She asked me to stay here.

We all believe him to be very honest.