There are specific dates given by the GMAC on which you can take your test.

Fee for the exam: $250 

There are three ways by which you can register for the exam.

          Online By               Phone              By Mail 

ONLINE :

For the fastest and most convenient service, register online. You can get the online form by visiting the learners and test takers section of the GMAT website at www.mba.com. A valid credit card is required (American Express®, Discover®, JCB®, MasterCard®, or Visa® card), or an electronic check (e-check) if you have a bank account in the United States or its territories.

Registration is open 24 hours a day, 7 days a week.Click Here for online Registration

BY PHONE :

A valid credit card is required (American Express®, Discover®, JCB®, MasterCard®, or Visa® card), or an electronic check (e-check) if you have a bank account in the United States or its territories.

When registering by phone, you are given a
Registration number, which you must bring to the test center on the test day
Test date
Reporting time
Test center address

The Contact details are as follow:
Telephone: +603 8318-9961, 9:00 a.m. to 6:00 p.m. AEST
In India: +91 (0) 120 439 7830, 9:00 a.m. to 6:00 p.m. Indian Standard Time
Fax: +603 8319 1092

BY MAIL :

To register for the GMAT® exam by mail or fax, you must complete the GMAT® Appointment Scheduling form. To complete it, you will also need the Country Code List. If you wish to fax your form, please use the fax number for Customer Service in your region listed above. If you wish to mail your form, please send your completed form to:

Pearson VUE
Attention: GMAT® Program
PO Box 581907 Minneapolis,
MN 55458-1907 USA