To save a Beyond CAD project, click on 'File' in the top menu and select 'Save'. Enter the desired save name and it will save the Beyond CAD project as a .bcad file in Windows. If the file has been saved previous, selecting 'Save' will simply overwrite the previous saved file. If you want to save a file with a new save name so as to not overwrite the previous save file, select 'Save As' from the File drop down and enter a new name to save the file as.
Note that Beyond CAD DOES NOT auto save.