no
Yes.
Not without a prior agreement, otherwise it violates the tenant-landlord laws. If you are just moving into a two bedroom apartment and there is a separate listing for one of the other rooms, yes they can. If they decide to go and rent out one of the other rooms when you are already living there, then they can only do that if you and your landlord are at a mutual agreement. Otherwise, they cannot. Don't worry, as long as you are paying the rent on time, they can't evict you for disagreeing with their plans. And if they try, you can sue them for it.
Landlord
It depends on where you live, but usually, you first visit the place you want to rent. If you like it, you take arrangement with the landlord, sign a contract, and usually, you are now the tenant of the house/apartment/room.
Room for rent or just simply boarding house.
Technically, no matter how old you are, unless you have a rent agreement or lease (which prevents search and or seizure by the landlord) with your parents, then they can search your room anytime they want if it is in their house. A rent agreement doesn't include you helping to pay bills if you have a job.
Basically anyone you rent a room from IS your landlord. Now, if you're talking about renting a room from someone who happens to be renting from a landlord, it depends on whether that landlord allows the tenant to rent a room to someone else (this is called subletting). I would be very careful about renting a subletted area from a renter. As a subletted renter you dont' have any rights as you would if you were a normal renter. The actual landlord may not allow the renter to sublet, and the renter could be kicked out, as can you!
You can rent out a room or part of the house, or you can rent the entire house. Either way you can run an ad or listing with a real estate or rental management office.
Call the local health inspector.
You'll find this to the right of the room.
Usually you do... if not that's prettty jacked up...
Finding a room to rent depends on many things including how long you want to rent, where you want to rent and the type of room you are looking to rent. You can visit a site like hotels.com and search for exactly what you are looking for. Also, check craigslist.com if you are looking to rent a room from someone's house. You can find rooms at discounted rates on Priceline.com or Travelocity.com and specity the part of New York you are looking for. If you know of a specific hotel you are interested in, you could also call them and book a room directly.