Hi John
Best thing with any kind of finder is to align it in the daytime. Find an easily identifiable object such as a chimney or lamp-post in the main telescope. Then look through the finder to see if your red dot is centred on the same thing you can see in the eyepiece. If not, then you need to adjust the screws on the finder until the red dot is in the right place.
As to actually using it, we have sometimes found that when people come to us with problems using red dot finders, sometimes they are looking through them slightly crooked instead of straight through. If there are two rings forming your finder, you need to make sure that they are lined up when you look through, like a gunsight. With a red dot finder, I personally find it easier to use with one eye, as you can only see unaided eye stars with them. With a magnifying optical finder, it helps to keep both eyes open because you see many more stars with an optical finder.
If you still have trouble, you could always it along to one of our meetings of the
North Essex Astronomical Society. You could bring it to one of our public lectures (next one is on Weds 18th July) or one of our public observing events at Great Notley Discovery Centre (next is a solar observing day on Sat 21 July at
midday). One of our members will be more than happy to give you a hand. Details are all on our website.
Hope that helps.
Rachel
