From #openttdcoop wiki
There are three usual layouts;
One-way ML: "Bus-stop"
So called, as it resembles off main-road bus-stops, trains filter off the one way ML, into the Station, and back on further up. Simple
Two-way ML: Turnback Loops
These usually get split into two halves, one either side of the Station. They take trains coming from one direction, pass them to the station and send them out back the way they came from. These lend themselves to side-by-side RoRo stations quite well, and providing the network topology is right, work very well.
Two-way ML: All to all
These will usually get one big junction, but can often get one either side, like it's Turnback cousin. They take trains form both directions and feed them into one large station complex. These can be useful when the network topology makes the route back to the source quicker on a different path than the one it came from.