Most algorithm analysis courses at Universities are only open to upper level undergraduates and graduate students. Why would you expect this topic to be easy to learn? There are algorithms that are simple to analyze and the Wikipedia article on Big O notation is probably adequate to understand how and perform an analysis on them, but doing an analysis on any reasonably complex algorithm is non-trivial. The Cormen book is probably the most widely used book on algorithms, but I wouldn't consider learning algorithm analysis from it or any other book painless.
