What is the difference between mindfulness and concentration? Does the concentration occurs during first jhana?or is it relates to the samadhi which involves in second jhana?What is actually one pointed of the mind means?
Concentration is part of every mind state: the normal, regular, every-day-of-life mind states; the unwholesome ones; the wholesome ones.
It is absolutely not limited to jhana states!

One-pointed means basically that it focusses the entire mind on to an object. In vipassana we speak of momentary one-pointedness where the mind in this moment focusses entirely on this object and the next moment on the next object.