The Expat Guide to Greece is the best place to start. It has a section in visas that is helpful.

There is no uniform Schengen Visa for visits longer than 90 days. If you wish to remain in any country in the region longer than 90 days, you must apply for a residence, work or student visa directly through the embassy or consulate of the country where you wish to settle. However, the Single Permit Directive allows immigrants who are legal residents of an EU country and those who are seeking residence permits to apply for a residence and work permit for that country through a single application process.

Depending on your chosen country and your personal circumstances, you may need to apply for a long-term visa before traveling to the region. However, once you have obtained a long-stay visa for one country within the Schengen Area, you may travel to any of the other countries within the Schengen Area for up to 90 days within a 6-month period without applying for another visa. Once you have resided in one country within the EU continuously for at least five years, you may be eligible to apply for long-term resident status, which carries similar rights as those enjoyed by EU citizens, including access to social services as well as the right to travel and work freely within the EU.