and I appreciate the help the website is doing
and I just wonder when I wan to make a circle in a sketch there is a choice of the circle to be construction, what is used for ?
Construction geometry will not be part of an extrude/revolve/cut. It is used a reference only.
i would really recommend looking at some tutorials and some youtube videos.
For construction lines give this video a look:
solidworks Sketch Construction Geometry - YouTube
you can turn any sketch entity into construction geometry by using the construction tick box
Construction Geometry whether it be circles, lines or whatever is usually used to help with the creation of other geometry.
Take a look at this video.
It's old but it will give you a good overview of construction geometry.
Hope this helps.
Any sketch geometry can be used as construction or be converted to construction, not just circles. If you were to convert one of your extrude cut circles to construction, it would not be seen by the feature & so the hole would not be cut. It can be used in this state as a reference, for positioning other geometry, centre lines, mirror lines etc.
See this help file:
2015 SOLIDWORKS Help - Construction Geometry
Retrieving data ...