Myers-Briggs Type Indicator (MBTI) is basically used as a psychological test to identify the personality type. It has identified that there is a preference for using either the judging function (thinking –logical or feeling-empathetic) or perceiving function (sensing –concrete or intuition-abstract) when people map to the outside world.
An illustrative diagram of the chart is given below:
Suppose a person is of ENTJ type, it means that ENTJ is extroverted, J indicates their dominant function, i.e., extraverted thinking is their preferred judging function. ENTJ introvert type, the auxiliary perceiving function is the introverted intuition. However, for INTJ, it is introverted, hence, the judging is auxiliary function which is preferred judging function and the dominant perceiving function is the introverted intuition.