How to learn to analyze sites?

Question

Analytics

There is a great desire to learn how to find problems in sites. It is to look for flaws, errors, to try to determine what is causing this. In general, everything related to the analysis of the site. There is good knowledge in html, css, but absolutely no knowledge in java, php and others. I would like to ask if there are any good books, projects that will help you immerse yourself in this atmosphere? It is in the course of learning other languages ​​that you try to consolidate the lesson through tests / checks. And what you need to know (I'm talking about languages). Are there any good platforms to try to inject any sql, php and other injections found by site analysis?