We often use an infinitive to talk about a person's purpose — why he or she does something.

• I sat down for a minute to rest
  
• He went abroad to forget
  
• I'm going to Austria to learn German

In a more formal style, we often use in order to or so as to.

• He got up early in order to have time to pack.
• I moved to a new flat so as to be near my work.

In negative sentences, we nearly always use the structure with so as not to or in order not to.

• I'm going to leave now, so as not to be late. (NOT I'm going to leave now, not to be late.)

I am to...     you are to...     etc

1) We use this structure in a formal style to talk about plans and arrangements, especially when they are official.

• The President is to visit Nigeria next month.
• We are to get a 10 per cent wage rise in June.

2) We also use the structure to give orders. Parents often use it to children.

• You are to eat alt your supper before you watch TV.
• She can go to the party, but she's not to be back late.

3) You can often see be + passive infinitive in notices and instructions.

(noun + is) + passive infinitive (= to be + past participle)

• (This form is) to be filled in in ink.

Sometimes be is omitted.

• To be taken three times a day after meals, (on a medicine bottle)