Click Save in the Standard toolbar or select File 
Save Save... (or press CTRL+S). A message appears in the status bar to confirm that the document is saved.
Please note: this information is without using Teamcenter or any other PLM system with NX.
Using Save will only save the active Work Part.
More about the Save command
Using the Save command will only save the active Work Part. The Work Part is in regards to the active Assembly or Model. Users can double-click on either to specify the Work Part or right-click on the part or assembly and select Work Part.
•Specifying a part as a Work Part will save that individual part.
•Using Save will not save all modified files in the assembly.