A sociologist is that person who studies sociology and is mainly dedicated to studying the life of human beings within the groups in which they develop.
One of the main things that sociologist do is to investigate the processes carried out within society, such as it´s structure, problems, behaviors among others.
Another is to develop theories according to the research carried out, after making a rigid diagnosis of the situations studied, as well as an evaluation and development of measuring instruments. It´s important to mention that the results of these investigations will always be communicated.
So, the answer to this question is that all the sociologist do in their studies investigation and develop theories acoording that investigations.