The simplest method of transfer to the rotation wheel is similar to what is shown in the movie 2001: A Space Odyssey. The rotating ring is within a non-rotating outer hull. One side of the hub is an open ring through a bushing and into a tube; the other side is a central axle. Near by, behind the axle side, is the counterrotating flywheel.
The tube entry actually is long enough to float into; a meter, maybe 2, and on the ring-side wall, a series of ladders run down to the "gravity deck." The ladder positions are marked on the insides of the transition tube, and have recessed handholds along the ladder lines.
From the airlock section, one floats into the transition module, stops using a handhold affixed to the non-rotation portion but extending into the transfer tube section. While stopped, one waits until just before a ladder mark is "down", extends hands to grab a handhold, and then crawls, feet first, face to the side of the tube, into the rotation wheel. Swinging the feet down, one transitions to the ladder, maintaining downward pressure with the hands at first, but as one descends, acquiring more and more gravity, until one is on the deck.
To exit, one climbs the ladder, and at the hub, pulls out into the transfer tube, grabs the non rotating handle to stop rotation, and floats forward into the non-rotation section of the transfer tube.
Since the entire system is in a single pressure container, with no external moving parts, it's simple for the astronauts, and reasonably safe. It does, however, require on-orbit assembly.
A ring that rotates with it's own vacuum capable rotation ring is mechanically more complex, but less massive, and easier to pack.
Note that items dropped from the hub will appear to acquire antispin velocity to a person on the deck, so baffles might be needed; anything dropped will hit the antispin baffle, and accelerate down it until it hits. The use of the ladder is as much to accelerate one as to allow egress.
Note that some form of dynamic load balancing is advisable, as well, since an astronaut climbing or descending the ladder changes the balance. Water is a likely candidate.