تويت
LET'S START 
Before
Before is used for something that occurs before a certain time.
For example
For example
We should finish this exercise before 4.00
I need to buy a present before James comes
Before starting any business, it's a good idea to write a business plan
Note that when a preposition is followed by a verb, the verb ends in ing.
So for example
So for example
Where did you live before comingto America? Correct
Where did you live before to come to America? Incorrect
After
After is used for something that occurs after a certain time.
For example
For example
I'll see you after work
Camilla won't be home until after midnight
David got promoted after just two years with the company
As - Time
As is used when two shorter actions happen together.
For example
For example
I dropped my keys as I left my apartment
As is also used when two longer actions happen together.
For example
For example
His health improved as he exercised more
As time went by his English got better
As is also used when an action happens during a background situation
I woke up as the sun was rising
She arrived as you were leaving
As - Reason
As is often used to show one thing is the cause of another, like the word "because".
For example
For example
I'm going to bed early as I have to get up early tomorrow
As we're not busy, let's meet this afternoon for lunch
As soon as
As soon as is used when something happens immediately after something else.
For example
For example
I'll give you a call as soon as I'm finished
As soon as they go out let's eat lunch
We'll send payment as soon as you fax the signed contract
(C)
i just started understand it right now 
So ,, thanks alot teacher Marshmallow
yes you are right , we are as Arabs bad in english grammer
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