OpenSCAD tutorial
Trying out OpenSCAD by following this tutorial -- https://www.youtube.com/playlist?list=PLMVZLVfQsAUkBLKa6ziRO6dMGEMsw9-i3
Refresh display -- press F5
For exporting to STL, firs render the object by press F6 to render, then click on 'Export to STL'
User Manual
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/2D_to_3D_Extrusion