Those two functionnalities are very similar since they use the corresponding Solr basic functionnalities that rely on a text file.
Unless it has been modified, those text files are located in the conf folder of the FileShare core.
The Admin UI allows the user to see and modify the files.
The syntax for the synonyms is as follows :
i-pod, i pod => ipod, sea biscuit, sea biscit => seabiscuit
The syntax for the stopwords file is the following one :
a an to from
To prevent two people from modifying the same text file at the same moment, the servlets dedicated to these functionnalities use a mutex semaphore. There is also a list_language.txt that you have to fill, which defines where to apply the semaphores.