Well? Do you? If your response is 'call a tyre fitter', it may be time to do some swotting up as not only is waiting around for an emergency tyre fitter not much fun, you may find yourself somewhere out of the way waiting days rather than hours! And what if you are in a hurry to get somewhere you absolutely HAVE to get to? Life would be much easier in this situation if you knew how to handle your flat tyre yourself.
Shockingly, some drivers don't even know whether or not they have a spare wheel! If you do it is generally kept in the boot, but in some cars that may be in the front of the car (my old MR2 had no boot to speak of and the spare was stored at the front of the car).
It is common these days to have a space saver spare rather than a full sized one.
The idea of this is that it can (slowly) get you to where you need to be in an emergency, but for the 99% of the time when you don't need it, you have more storage space).
Wherever it is, you should know and be able to access it yourself.
Next you will need some tools.
It is no good storing these somewhere safe at home! They need to be kept with the spare itself, and you ought to know how to use them.
Not sure? Read the manual! Some car manufacturers don't offer any kind of spare, but only a puncture repair kit.
This is not ideal as there will be many punctures that can't be easily repaired in this way, but if it is what you have, you should still be familiar with how to use it, and have an idea of what you will do if you find yourself with a puncture you can't repair, or two wheels punctured! Whatever equipment you have in your car to handle punctured car tyres, you need to make sure you understand how to use it.
If you aren't sure, and reading your car manual doesn't help, why not ask the tyre fitter next time you are having tyres replaced? They will be familiar with the tools you need (and should have!) in your car, how to use them and can give you step by step instructions for changing the wheel with the puncture for the spare wheel.
Having the confidence to know what to do in an emergency is the first step - panic won't help anyone! Hopefully, your preparation will never be needed, but it's better to be safe than sorry!