Go to insert>model datum>plane or click on the datum plane tool icon and the datum plane creation dialogue box will appear. Now you will be selecting sufficient numbers of references.
Say you want to create a datum plane which will be parallel to an existing plane or surface; select the plane or surface which the datum plane will be parallel to and then the translation field below will be activated. Enter the offset value between the surface/existing plane and the new datum plane.
Similarly, if you want a datum plane to be passed through an axis and create a certain angle with another plane then you select the existing plane and the axis as references; the bottom translation field will change to rotation and you will be entering the rotation angle there.
Until the required numbers of datums has been selected the OK button won’t become activated.
Please notice the second tab (display) of the datum plane creation window, if you go to this tab, you will be able to define the size of the datum plane you have just created.
In the properties tab of the datum plane creation window, you can change the default name of the datum plane; alternatively you can right click to the datum plane in the model tree and change the name.