I'm told that the following book will almost assuredly provide you with a comprehensible introduction into the realm of critical thinking at a reading level that surely cannot be too far ahead of your own:
http://www.lfb.com/prodinfo.asp?number=CH8495&variation=&aitem=1&mitem=11
In the case that it is too difficult for you though just drop me a freepmail and I will happily point you in the direction of a simpler text for your demonstrably simple mind.