How long will it will take to get cetified with the beginnner diving course?

The first certification, if you want to be able to scuba dive everywhere in the world is the PADI Open Water Course. It takes between 3 to 4 days to do it. Most of the time 4 days are enough, depending on the skills of the student and the wish to rush it.

There is also the option to take the course online http://www.padi.com/elearning-scuba-registration/default.aspx?irra=21586&CourseType=ow which implies doing the theoretical part of the course and the exam directly to PADI (by clicking to the link). It is a good solution for students that want to study at home and go directly in the pool and in the ocean when they arrive. 

Discover Scuba Diving is not a certification but the first trial of scuba diving, and it takes between half a day to a full day of practice.