Perhaps you have some confusion between permanent residence (AKA Green Card, GC) and Citizenship? The usual train of events is as follows...
You need a visa to legally work in the US. This visa can take many, many forms. Some are work related, some are family related, some are investment related, some are marriage related etc.(look up for yourself). Almost all are difficult, costly, time consuming to get and have a queue of people and most employment related ones require a sponsor, which is difficult to find with so many US citizens in the running.
Once you have secured a visa (which must be a dual intent visa, i.e. permit immigration or adjustment of status), you will need your employer to sponsor you for the GC. Getting the GC can take from 6 months to 10 years, depending on circumstances.
Once you have held the GC for 3 years (for marriage) or 5 years (for employment) you should be eligible for citizenship. Again there are lots of conditions to being eligible such as being resident during that time, filing taxes, being a good boy and following the rules....
- Tim