I am attempting to study logic by myself. I acquired the book A Mathematical Introduction to Logic by Herbert B. Enderton. I want to ensure that this is a good introduction so, is this a good introductory book for logic? Would it be better to acquire other books?
This is a well-regarded book, much used as a course text over many years (though it is forty years old, and perhaps no longer the first choice at its level).
But -- an obvious point, but still worth making -- it will very much depend on your background (on your "mathematical maturity") whether Enderton's is the best first logic book for you. It's probably fine if you are some way into a mathematics degree and are used to rigorous formal thinking: probably not so fine if you haven't done much university level mathematics.
You can find out rather more about different books at different levels by looking at the Teach Yourself Logic Study Guide available here: http://logicmatters.net/students/tyl/