How exactly does positive psychology helps companies? Is it related to human resources?

There are also organizational psychologists, and we do employ some at my company. it is related to HR in that employing such people can help get a pulse on where the culture and organization need change.

Many of the 'best practices' used by Human Resources professionals were developed as a result of 75+ years of research by Industrial-Organizational (I-O)psychologists. That research was conducted in the field, that is onsite within businesses, and in the scientific laboratory. Positive psychology can enhance the workplace when it complements the work of I-O psychologists.

I like this definition of positive psychology that I found at yahoo answers: "Positive Psychology is the scientific study of the strengths and virtues that enable individuals and communities to thrive. This field is founded on the belief that people want to lead meaningful and fulfilling lives, to cultivate what is best within themselves, and to enhance their experiences of love, work, and play. " https://answers.yahoo.com/question/index;_ylt=A0LEVjhrOUNXyaUAHWMnnIlQ;_ylu=X3oDMTEyajU3c2g2BGNvbG8DYmYxBHBvcwMxBHZ0aWQDQjIwNDRfMQRzZWMDc2M-?qid=20100911141007AA61iXT

One of the goals of positive psychology is to " ...build a science that supports ...workplaces that foster satisfaction and high productivity ..." This was the second goal listed at the web address above. I-O psychologists are also interested in helping foster workplaces where there is job satisfaction within the workplace. So, the two disciplines overlap to some extent; I-O psychology has much broader goals than this for the workplace.

I hope this response helps you to understand the relationship between I-O psychology, positive psychology and some of what HR practitioners do on a day-to-day basis.