SelectionEvaluateCreateCell[notebook] takes the current selection in a notebook and creates a new cell containing the result obtained by evaluating the contents of the selection using the kernel.
SelectionEvaluateCreateCell[notebook, sel] sets the current selection after the evaluation to be as specified by sel.
The first argument of SelectionEvaluateCreateCell is a NotebookObject.
Possible settings for sel are as in NotebookWrite.
The default for sel is After.
SelectionEvaluateCreateCell[notebook, All] sets the current selection to be the cell corresponding the result from the evaluation.
SelectionEvaluateCreateCell performs the same underlying operation as typing Shift-Return in the front end. It does not, however, have side effects such as incrementing $Line.
See The Mathematica Book: Section 2.10.3.
See also: SelectionEvaluate, SelectionCreateCell, NotebookRead, NotebookWrite.