To save your score choose:

File → Save as...

Choose a file name on dialog and press OK! The default suffix is .ntd.

To save a file which was already stored before choose:

File → Save

To restore a previous saved score choose:

File → Open ...

Choose a file name on dialog and press OK!

To start with a totally new (empty) score choose:

File → New

To terminate the program choose:

File → Exit