You have 2 choices:
db.users.find({"name": /string/})
or
db.users.find({"name": {"$regex": "string", "$options": "i"}})
On second one you have more options, like "i" in options to find using case insensitive. And about the "string", you can use like ".string." (%string%), or "string.*" (string%) and ".*string) (%string) for example. You can use regular expression as you want.
Enjoy!
