Saving a document can be done from a the Standard toolbar using 
Save icon, from File pulldown menu, or by selecting the hot keys Ctrl+S, but only the pulldown menu gives you all four save options: Save, Save As, Save All, and Save Management.
Documented topics:
Save - Overwrites existing document(s) at the same directory.
Save As - Allows change of the name directory.
Save All - Overwrites existing documents at the same directory, when in an assembly.
Save Management - Allows management of specific documents in an assembly.
Save Send To Function - Saves the model into a user selected directory.