Not to be advertising but go to
www.ar15.com. It is a real informative site about any type of gun you need, including my favorite AR-15. Just go to the handgun section and read up.
Single action or double action? Well this refers to the action of the hammer. A single action in simple terms only has one stage of the hammer. Where a double action has two stages.
Now there are harmerless guns and guns with internal and external hammers. There is just to much information to elaborate on. Any other questions let me know.
I do suggest starting off with a 9mm for someone who has never owned a pistol just because of the low recoil. The low recoil improves accuracy and it also has plenty of stopping power. Just don't go with any lower caliber such as a .380 or .22. Just not enough punch.
EL