I import a CSV File and for each coordinate, I get a point in the map. Can I set a column for the value. Then the size should based on the value have a special size. Or based on all values, it should display from max to min value.
In QGIS go to Layer Properties -> Style.
Either use 'Categorized' if you have a few values, 'Graduated' to be based on all the values (size is under the advanced menu) or create your own rules using 'Rule-based'.
See HERE for duplicate question (comment from Joseph).