As

Dave works as a clown or Dave works like a clown?

For an explanation of "like" and "as" click on the link above.

As she was leaving the phone rang.

Since she was leaving at the same time as me we decided to take a taxi together.

For an explanation of "since" and "as" click on the link above.

As I was leaving the house I met my neighbor.

While we were talking the postman arrived.

For an explanation of "as" and "while" click on the link above.

Collecting things, like stamps or coins, can be a good investment.

Collecting things, such as stamps or coins, can be a good investment.

For an explanation of "like" and "such as" click on the link above.

As .... As

As is used to compare equal things.

He works as hard as she does.

English is not as difficult as you think.