One bedrooms don't have a studio part. You enter from the hallway into a combination living room/kitchen. There is a sofa bed in the living room. Off of that is the master bedroom with a king bed. The bedroom and the living room area both have doors into the bathroom area (so someone sleeping in the sofa bed doesn't have to come thru the bedroom to use the bathroom).
A two bedroom unit is a one bedroom unit with a studio added on to it. Some two bedroom units are "dedicated 2 bedrooms" which means they can only be rented out as 2 bedrooms. Those have only one entrance to the outside - in the front hall area. There are also studios and one bedrooms that each have an entrance door from the hallway and a locking door between them. Because these can be locked off, the one bedroom part could be rented by one guest and the studio part can be rented by another guest. Or the door could be opened to turn the one bedroom and studio into a 2 bedroom unit.
Here's a link to the official Disney site page with more BCV information and links to floor plans of studios, 1 and 2 bedrooms.