APA Style is a standardized format for writing that has been established by the American Psychological Association. It is generally used by students and scholars working within behavioral or social sciences. APA Style would guide you on how to:
Is there a tool in databases that can help me to cite in certain styles?
Yes, many databases have a built-in tool that could format a source based on a given citation style, such as APA. However, machine-generated citations often contain errors. You should make sure that you knows how to cite properly, and always double-check and verify that you cite your sources correctly.
DOI stands for a digital object identifier. It is a unique alphanumeric string assigned to an article that is available electronically. Consult "What is a digital object identifier" for more information.