Simple Present.

We use Simple present to refer to an action can be a habit, a hobby, a daily event, a scheduled event or something that often happens. It can also be something a person often forgets or usually doesn't do.

Examples:

The train does not leave at 9 AM.
When does the train usually leave?
She always forgets her purse.
He never forgets his wallet.
Every twelve months, the Earth circles the Sun.
Does the Sun circle the Earth?

Can also indicate the speaker when believes that a fact was true before, is true now or will be true in the future. It is also used to make generalizations about people or things.

Examples:

Do pigs like milk?
California is in America.

New York is a small city

Speakers occasionally use Simple Present to talk about scheduled events in the near future.

Examples:

The train leaves tonight at 6 PM.
The bus does not arrive at 11 AM, it arrives at 11 PM.
When do we board the plane?

Speakers sometimes use the Simple Present to express the idea that an action is happening or is not happening now.

Examples:

He has his passport in his hand.
Do you have your passport with you?

I am here now.

The diference between present simple and present continous is that the present simple is used to talk about things that you do usually and the present continous is used to talk about things that happen in this moment

Credits:

http://www.englishpage.com/verbpage/simplepresent.html
http://www.curso-ingles.com/gramatica-inglesa/psimple.php
http://www.languageguide.org/english/grammar/esp/part1/simple_present.jsp