Hello all.
I was just designing a web application form that is meant to accept a user's request to use a particular room in a specified period of time. After the user enters his specifications, the application now responds, telling the user if the location specified is available at the specified time. I have been thinking about this issue for a while now, but I don't even know how to start. Thanks in advance!

I would start by designing the database. You could create a table for just that room with fields for the user id or name of the person booking the room, a start time and an end time. Create a constraint on the table that prevents overlapping start and end times so that if some one wants to book the room and there is already a booking for the same or overlapping times then the database will not allow the new row to be inserted.
You would then create the web interface containing a form that accepts such things as the username or id, the start time and the end time. Or prompt for a duration and work out the end time from that in order to write a new row in the database table.
It would be nice to say who the room was already booked out to if the insert fails.