This will make a new sketch, so you will need to reselect the sketch from any existing pocket operations, if you want to use the new sketch.
You can combine sketches by selecting multiple sketches, then right-clicking and choosing "Combine Sketches".
If your pocket has islands, then combine the sketches into one sketches and use that.
A pocket operation can be added from the Machining menuThe pocket operation only has one sketch associated with it.
or by selecting a sketch, right-clicking anywhere in the Graphics window and choosing "New Pocket Operation..."The Pocket dialog will then appear.
If a sketch was selected when you created the operation, then it will already be selected in the dialog, in the sketches drop-down.
If not, you must select your sketch, by clicking in the "sketches" box on the down arrow, or by pressing the "Pick" button and clicking on your sketch in the Graphics window.
You must also select the Tool you want, in the "Tool" box.
For me, the default 3mm tool was selected.Check that the feedrate and spindle speeds are correct.
Also, set the depths to the correct value.
Clicking in a box will change the picture to show you the meaning of the parameter.
For example, in this picture I have clicked in "cut mode" and the picture is showing me the meaning of my choice of "conventional"
Click the "OK" button to confirm your parameters.
The pocket operation will be added to the "Operations" object in the Objects window.
When you post process, you will see the toolpath created by this operation.