Saving and using snippets is done just as any treatment.
Snippets are considered as treatments, and they must be saved as such.
To save the snippets, proceed as usual :
select File/Save Treatments As
choose a name and location
If you didn't save the snippets, AS will ask you if you wish to save them when closing the corresponding sound file or quitting AS.
To reuse the snippets in the file they originally belong to :
select File/Open Treatment
or Open Recent
and select the treatment
double click on the treatment file : the original sound file will open too
If you wish to open the treatment from a new file you will be offered to use the current file or to select the original file.