To find JSTOR, navigate to the library homepage; click on the link to Databases (in white letters under OneSearch). This will take you to the Databases A-Z page. Mango Languages is listed in 2 places on the Databases A-Z page: under the letter M and also at the top of the Databases page in the box labelled 'All Database Types' -> Language Learning.
If you are off campus, you will be automatically prompted to enter your Surf ID and password when you click the link for Mango Languages.
For more help, contact a reference librarian.