Someone must first petition the U.S. government on your behalf before you can get a green card as an employee or family member. This process is referred to as a visa petition.
The first step towards obtaining a green card is to have someone sponsor you. This could be a family member who is a U.S. citizen or a U.S. employer who wants you to work for them. After filing the petition, your sponsor is known as the "petitioner" and you become a "beneficiary". Once someone has agreed to sponsor you, they must file a petition to get the ball rolling. While family members would need to fill out a Petition for Alien Relative (I-130), there are a number of different employment-based petitions for immigrant or non-immigrant visas.
The petition is designed to demonstrate your petitioner's interest in helping you immigrate as well as prove your sponsor's right and ability to do so. For family members, this often means establishing that the relationship is legitimate (often through a birth certificate or other legal document).
If your sponsor is a company, it typically must prove that a labor certificate was granted, show that it can actually employ you (often by submitting tax returns), attach a list of degrees or certifications required for the job, and include any other information necessary to demonstrate its intent to employ you.
Finally, the petition will set forth how the application will proceed, whether through a consulate outside of the U.S. or through the USCIS (U.S. Citizenship and Immigration Services).
When the USCIS approves your petition, it sets your place on the waiting list. Some categories of immigrants only receive a certain amount of green cards per year, so establishing your place in line is extremely important. Other categories of immigrants, such as close relatives don't typically have limits on the amount of green cards offered.
The date your sponsor sent in the visa petition is your "priority date". It is advised that you check the State Department's website in the Visa Bulletin section to see which priority dates are being allowed to move forward with filing for a Green Card.
Immediate relatives such as parents, children, spouses, or minors of a U.S. citizen don't have priority dates and don't usually have to wait like those in other immigrant categories. If the visa applicant is already living inside the U.S. legally, the entire process can be expedited under what's known as an "adjustment of status". This procedure lets the entire process be completed entirely in the U.S. and can be accomplished much faster than normal. Applicants can even submit the adjustment of status paperwork at the same time as the petition. Note that immigrants who entered the U.S. illegally cannot normally benefit from the adjustment of status option.
Contact a qualified immigration attorney to help you with visa procedures.