To Define an ACS with Data Points

Select the Define ACS by Points tool (Drawing > Drawing Aids > ACS > Define an ACS split button).
Enter a data point to define the ACS origin.
Enter a data point to define the direction of the ACS's positive x-axis, which extends from the origin through this point.
(3D only) Enter a data point to define the direction of the positive y-axis.
The direction of the positive z-axis follows by applying the right hand rule.