If you have 'Discovery' enabled in your ServiceNow instance then you can save credentials in an encrypted form inside discovery credentials.

These credentials can be used to access a 3rd party tool through ServiceNow features such as orchestration/Discovery or can be used for internal use.

Use case:

Consider you have to access a 3rd party tool through ServiceNow (with or without using orchestration). Access to this 3rd party tool require userID and password which you have to store in a encrypted form and can be decrypted whenever required.

This blog will help you in how to store and access the credential using discovery credentials feature.

http://inmorphis.com/blogs/credential-storing-in-servicenow/