If someone adds you on Snapchat, there are varying levels of the content they'll be able to access based on your privacy settings. If you've set your account to Private, and the other user adds you but you don't add them back, they won't be able to see much about your profile. To change, or check these settings open Snapchat and navigate to the Settings page. Tap on the 'View My Story' icon and toggle between 'Everyone,' 'Friends Only,' or 'Custom. You can also change who can contact you, see you in the 'Quick Add' section, or who can see your location. Although you may not immediately know who just added you, you can control what others see by going through these settings.