I've selected my out from Glasgow train ticket time but I'm confused about how to book a return time a week later. Can I buy a one way ticket, if so I don't see how to do that. Thanks for guidance.
Assuming you are trying to book on the Scotrail website, on the top bar of the bookings window you should see the options Single, Return, Flexipass or Season in a row.
Return is the default setting. To buy singles click on 'Single' at the left of the bar.
Don't book more than 8 weeks before travel as that is when the cheaper Advance tickets are issued. Get those and there is no price difference between 2 singles and a return. Maybe 2 singles will be cheaper than a return.