The best time to align your finder is during daylight hours. Look for some distant landmark, like distant phone antennae, towers, buildings, what ever as long as it is a long way distant - being Earth-based you won't have problems of Earth's rotation. Point your scope to that target and using your lowest magnification (longest focal length eyepiece) locate the target in the eyepiece.
Your finder scope is then just a matter of patiently tweeking those thumbscrews a bit a time to set the crosshairs to sit on the centre of the target in your eyepiece. You can now also increase the magnification through your telescope to get a more accurate centering of the crosshairs.
Those thumbscrews ARE supposed to move only small amounts at a time. Otherwise fine corrections of the finder would be very difficult. Take your time. That is another reason why this is best done for the first time during the day, without the distraction or frustration of wanting to start viewing the stars.
Alpha Centauri is not a red star. The only blazing red star in that part of the sky is Antares. Alpha Centauri however is an interesting telescopic object as in a telescope it can be seen to be two stars very close to eachother. Alpha Centauri is actually a tertiary star system (a three star system, with a binary being two stars), with the third component called Proxima Centauri. Proxima is a very faint star and is actually the closest member of this system to us.
Alistair,
here is a good tutorial on using a planisphere you may find useful.