As – Like

1 As is a conjunction. We use as before a clause, and before an expression beginning with a preposition.

as + clause

as + preposition phrase

Nobody knows her as I do.

We often drink tea with the meal, as they do in China.

In 1939, as in 1914, everybody wanted war.

On Friday, as on Tuesday, the meeting will be at 8.30.

In informal English like is often used instead of as.

This is very common in American English.

Nobody loves you like I do.

2 Function

We use as, not like, to say what function a person or thing has what jobs people do, what things are used for, etc.

He worked as a waiter for two years. (NOT ... like a waiter.)

Please don’t use your plate as an ashtray.