book recommendation on functional analysis

You can start out with the book Introductory Functional Analysis by B. Daya Reddy.

I started reading it and was not able to stop because everything was so clear and rigorously defined.

This book is unlike any other book you find off of the shelf, which are filled with indecipherable notations that are not transferable beyond what that particular book teaches you. Instead, the book by Reddy is filled with practical yet simple exercises that you can deal with only reading what is contained in the text and nothing else. What is so amazing is that the material contained in this book is so transferable, after reading it you will be able to tackle any research paper at least at the engineering level.

It is truly the best book to start out functional analysis

The very best introductory text on functional analysis that exists is the classic Functional Analysis by Bachman and Narici. Using a background of only basic linear algebra and advanced calculus/elementary real analysis/honors calculus, the authors develop all the standard topics on function spaces clearly and simply, with many examples and exercises. Best of all,it's available from Dover,so it's very inexpensive! To me, this is the very best self-study text that exists on the subject and I'd heartily recommend it to any beginner.

Real and Functional Analysis by Serge Lang.

Functional Analysis by Walter Rudin.