solidworks mirror tutorial for beginners
Open a new part document and sketch a polygon like below on the top plane (if you don’t know how to sketch see the sketch tutorial)
Then extrude it -60mm
Click on the mirror button in the features tab.
Mirror window appears on the left. Fill it:
Mirror face plane: select one of the visible sides of the part
Features to mirror: select boss-extrude 1 from design tree
Check the preview