>>527323893
Sections sections where the trains start are bidirectional tracks. the two tracks in the middle can fit a single train each, and are meant to be one directional. These are called sidings
Objective is to have the trains move off their bidirectional tracks and onto sidings, freeing up the way for the other train to get through.

First step is to force each train into a siding: Look at the red train, block it off one siding with a one-way signal opposite it. Then section the other siding off the green train with another signal that would let red move on to the track if green weren't in it. That's figure 1, the train having moved to the siding because that's as far as it can get before getting blocked.
And by virtue of symmetry, you've accomplished the same for green too.

Step two is to let each train off their sidings and back on track. That entire green line in figure 1 is currently "occupied" by green, even if green is physically contained wholly inside it's siding. So, put a signal sectioning it and it's siding off the bidirectional track, letting red through as the track is now properly free. Once red has moved off it's siding, both the siding and the rack will be free, letting green through. Success.

But, there's no need to have green wait for red to haul ass when red is already physically contained within it's own siding. So, put a signal for red too. That's figure 2. Just make sure these last two signals you put don't block trains from entering their assigned sidings