It's not that difficult once one has done it once

Start by making the view where you want the breakout view the active sketch view, draw some curve ( Spline) around the area. Finish the sketch and start the breakout section view.
toggle "Create" mode.
pick the view to section, next button:
pick the depth of the cut ( imagine the area that you enclose will be extruded from this pick, i.e if you have a second projected view you can pick in there to indicate the depth of the cut.)
Next button
( this will display the normal direction of the section view, unless you are doing something special, just click the next button
and select the curve that will enclose the area.
IF the curve-s is closed ( encloses an area)press Apply
If the curves are open ( such as a single s-shaped Spline) - click the last button "Modify boundary curves", you can then click-drag the small arcs that appear to form the area that you desire to cut. If you drag an arc to an endpoint it will disappear.
Regards,
Tomas