A few slots in the table gadget concern row selection:

selection	if set to a model, the values of the currently selected row or rows, as determined by a row-value call to the renderer, is stored in this model. See Models.
selection-index	if set to a model, the indices of the currently selected rows.
selection-required?	if set to a true value, the table ensures that some row is always selected, if the model is non-empty. If set to f, a state where nothing is selected is permitted to occur. The default is f.

Some words for row selection:

selected-row ( table -- value/f ? )

(selected-row) ( table -- value/f ? )