Here's how the process goes:
1) You need a sponsor in the US, either family or an employer. In other words, you need someone who can vouch for you having a reason to stay in the US on a permanent resident basis.
2) This sponsor needs to file either an immigrant visa petition to the US Citizenship and Immigration Service or a labor certification request to the Department of Labor. From this your sponsor should receive an immigrant visa number, which means that you have an immigrant visa available, which you need for the green card application. These immigrant visa numbers are on a preference system based on the country you are applying from, and whether or not you have relatives who are US citizens, as well as other factors.
3) Once you have a proper visa and a sponsor, you can fill out the application for a green card, which can be found on the USCIS website.
I hope this helps you out. Good luck to you!