This system uses train interrupts. For example trains for iron plates have iron plate loading station in schedule and an interrupt - if train has cargo -> go to iron unloading station until signal from station or empty cargo or 5 sec of inactivity. To operate it you need to connect top right AC to buffer chests; and connect bottom right AC to all inserters that unloading train and set them to read pulse mode.
Max in chest - how many items for station to be full (It will be full until there s less items than Min in chest value) Min in chest Item - self explanatory How many items per cycle - how many items for station to be serviced (if it s not full)