Like имеет значение "похожий на что-либо, подобный чему-либо". Используется для сравнения.

He speaks like a native speaker. - Он говорит, как носитель языка.

She looks like a celebrity. - Она выглядит как знаменитость.

Reading this book is like speaking to an old friend. - Чтение этой книги - это как беседа со старым другом.

As - это "в качестве". Кто-то ЯВЛЯЕТСЯ тем(чем), с кем (чем) сравнивают.

She works as a secretary. - Она работает секретарем.

The sea can be used as a source of energy. - Море можно использовать как источник энергии.

She used family photos as the only decoration of her walls. - Она использовала семейные фотографии как единственное украшение своих стен.

Сравните:

She speaks like a teacher (она не учитель).

She speaks as a teacher (она учитель).

AS + предложение

You must do as I told you.

AS IF как будто, будто бы

You behave as if you’ve gone crazy!

Упражнение:

1)After university I had a job __ a waiter for 2 months.

2)He behaved __ a fool and we got lost in the forest.
3)Why do you talk to me __ I were a child?

4)She is eighty but she behaves __ she were much younger than she is.
5)What are you cooking? It smells __ Indian food.
6)You look terrible! You look __ you have seen a ghost.
7)She sings __ an angel.
8)I'm much better __ you can see.
9)My sister is not at all __ me.
10)My daughter is just __ my sister.
11)I use one of the bedrooms __ an office.
12)You are very much __ your mother.
13)I hope to qualify __ an engineer.
14)My friend Rob looks __ John Travolta.
15)There is too much traffic in London __ in New York.
16)We're late for the train. We'll have to run __ the wind.
17)I'm your friend and, __ a friend, I advise you to think again.
18)I don't know you as well as he does but, __ your friend, I advise you to think again.
19)I want to join the air force __ a pilot.
20)We need a strong leader __ Winston Churchill.
21)I've done the work __ we agreed.
22)I was sure, __ was everybody else, that you would do well in this job.