You need to take the GMAT exam as it is one of the factors which all the management institutes in North America consider to evaluate you for admission into the MBA program. The test is conducted and designed by GMAC (Graduate Management Admission Council). You can prepare for the exam by practising sample test papers. Get hold of the GMAT Official Guide (prepared by GMAC) which consists of sample questions for your practice. The Official Guide is a must to solve before taking the exam. You must also join online student communities like http://www.igotdinged.com where you can meet other GMAT aspirants and pass-outs. These online communities help a lot because you get help from a number of people worldwide. Hope that helps..
I agree with you Sophie. I recently visited that site because my daughter plan to study in North America and she really needs good advices. I don't have enough knowledge about it so I have to seek help through the net.
You have to clear GMT exams with good marks first of all.And then,you could fulfill further formalities.And I think,you should take an advice from experts for that.