Hi Sarah
You will need some mountboard and tape, of course. If this is a one-off, then you can buy them from a shop which sells artists' supplies. Or if you can wait a few days, you have the option to participate in the club's annual mountboard order which closes next Wednesday.
viewtopic.php?f=2&t=2840It is possible to cut mounts by hand, using just a sharp knife such as a scalpel and a credit card to angle the knife when cutting the bevel for the aperture. I did my first ever mount that way. It took ages, involved a lot of cursing and the end result was not that good. An exercise in frustration, although I did manage to retain all my fingers at least. It is definitely a skil which requires practice to develop.
A better option is to use tools designed for the job. Some club members use equipment from Logan, which is reasonably priced. After my initial experience, I bought a mount cutter from Longridge at the annual photography show in Birmingham, taking advantage of their show offer. The expense will probably not be worthwhile if you only require this one mount, but any picture framer will be able to cut cut a mount for you. My neighbour has a picture framing business and he showed me his professional mount cutter. It cost several hundred pounds, the payoff being that he can create a mount in just a few seconds. Very impressive.
Alternatively, provided the mount you require is not bigger than A1 and you do not want to invest in the tools at this time, you can pop over to my place with your picture and I will give you a demonstration of mount cutting using the Longridge.