To apply for an MBA in the US, you'll have to first give either GMAT or GRE. Giving these exams is compulsory for students who wish to study abroad. Additionally, the procedure to apply for an MBA in the US varies significantly from B-school to b-school.
You'll need to apply to each B-school separately. Besides the GMAT/GRE score, you will also need to compile a number of other documents such as academic transcripts, LORs, SOPs. and any other relevant paperwork.
Most B-schools in the US have now developed online portals for uploading of the documents, so there is no need to send the papers by post. After looking at all the relevant paperwork, most importantly, your essay/SOP, the B-school will invite applicants for an interview. The interview can be given on Skype, so no need to panic.
Best of Luck!