You need evidence one of the following points (1, 2, or 3):
1) Master's degree and an employer in US willing to sponsor you
2) Bachelor's degree, 5 years of experience in the field, and an employer in US willing to sponsor you
3) If you want to apply under the national interest waiver you need at least 3 of the following (in this case you can sponsor yourself, you do not need an employer):
a) Diploma or certificate from a college, university, or a school.
b) Documentation proving at least 10 years of experience in the field
c) Professional license or certification.
d) Evidence that you commanded a salary or other reward for services that demonstrate your exception ability
e) Membership in professional association(s)
f) Recognition of your achievements and contributions to your industry or field by your peers, government entities, or professional or business organizations
g) Other comparable evidence of eligibility is also acceptable.
Now if you're trying for points 1 or 2, the employer in US would need to start a process for what is known as labor certification, they need to do a get a wage determination from the dept of Labor and prove that hiring you would not undermine wages of people already in US, conduct an employee search for at least a month and so on and so forth. This while process can take up to 18-24 months. Once that is approved they file I-140 with USCIS, which in turn takes about 6 more months to be approved. After you're approved the consulate will contact you about an interview that you'd need to attend to receive your visa.
If you're doing point 3 then you need to file I-140 with all evidence of your eligibility. If approved (NIW isn't too easy since it has a ton of requirements), you'll be contacted by the consulate about an interview in which you'd have to receive to get your visa.