I don't have screenshots nor can I tell you what the buttons mean, but the captions will help.
1) When the operator from the single track asks for permission, respond to him saying that he is authroized (follow the prompts if AI, and if not AI just chat with them or talk with mic. If the arrow is in the worng direction click on it and you will need to select the option that changes direction.
2) Once the AI operator has this confirmation you will see a flashing arrow. Click on this.
3) Now here is where you will just have to read your options. Once you click the arrow at the top a bunch of options come up. Look for the one that accepts the request. When you do this this will finalize the operation and the train will begin to approach. You can then hold him, or clear when the line is available.
When you requie to send a train to a single line section if it's AI you can skip some of these steps as the AI can handle things, however if you go by the book this is what you should do.
1) Click on the button on the phone for the AI operator and ask permission to enter (this can also be done with a human like above).
2) Once operator accepts click on the arrow and select the request options. Again you have to read this and see what optoin does what.
3) The Arrow will start to flash and will turn solid once the AI has allowed entry. From there you can send a train down this line.
Hope that helps.
Sean