What constitutes virtue and how to train myself in virtue?

It is said that Virtue is the ultimate weapon . It is also said that virtue automatically leads to enlightenment without any volition or desire to achieve enlightenment . Therefore I want to develop 'heightened' virtue but I am unable to find any sutta which explains what constitutes Virtue. In the following quote from AN 3.90 training for heightened virtue is mentioned: > “And what is the training in heightened virtue? There is the case > where a monk is virtuous. He dwells restrained in accordance with the > Patimokkha, consummate in his behavior & sphere of activity. He trains > himself, having undertaken the training rules, seeing danger in the > slightest fault. This is called the training in heightened virtue. My questions are : 1. What constitutes virtue ?(Any reference to Suttas would be great.If there are any books giving short summary of Patimokkha in English then that would also be great.) 2. How to train myself in virtue ? (Are there any training books available?)