It depends on the situation. If you are the previous owner and bank foreclosed on you, they will start the eviction process, however, often times they offer the occupant cash for keys to expedite the process. If you are in a rent controlled property, no cash for keys will be offered. If you are a tenant with a valid lease, you, the tenant has the right to live in the property until the lease expires. If you are on a month-to-month lease, new owner must give you a 90-day notice to vacate. There is no obligation to give you cash for keys, however, that can be an option to expedite. If you are pursuing a short sale, there is a government program that offers $3000 assistance if you are still living in the property and meet their criteria.
Whomever now owns the property will most likely be in contact with you soon, either by mail or in person. You do not need to seek them out and contact them, however if you don't have a lease or are the previous owner, you should start looking for new housing.