I would like to learn the subject 'complex numbers'. My goal is to study this on my own. Are there any good tips, books, sites to study this?
I suspect that the question may be starting from the point of "what are complex numbers" (far below the level of complex analysis). For that purpose, Wikipedia: Complex Number is a perfectly acceptable article with plenty of information.
If you're more of a video-type person then Khan Academy: Intro to Complex Numbers might be satisfying for your purposes.