I have doors like these that are closed and locked by a deadbolt.
Per the other posters, the lock is a deadbolt, which uses a key on the outside, and the inside can either be a key or knob. If you leave the house without a key, it cannot be locked except from the inside.
The door is kept closed when unlocked, by devices such as these Ball Catch. These ball catches are placed on the top edge or the opening edge to provide fiction to hold the door close.
In a heavy wind, the door may still be blown open
per the other question -
The question. If you leave the house, with the door unlocked, and decide to re-enter the house without having the key, then how will you open the door? With a classical door, you rotate a moving handle. But with these, the handle doesn't seem to be rotatable.
The door is held shut by the catch ball, to open you just push on the handle or door.