Computational activities are activities that when executed takes a value as specified by the expression found under Advanced in the Options menu:

The “Computations” field is an expression as defined in DCR engine expression language. An example that use computational activities can be found in this DCR Process Model:

When the user fills out the “Integer” field in the Form and then the Robot calculated Activity6, Activity0 or Activity1 might be included depending on the value entered in the form. Entering 8 will not include anything. A value less than 8 will include Activity1 and a value greater than 8 will include Activity0.
Computational values in a DCR Form
You can also use computational values in a DCR Form. Please check out this example for detail.