Many users are
always wondering about how to lock apps on iPhone, iPad and iPod touch. We
wanted to lock applications for privacy which might be very personal so that no
one can access without our permission. If you are already jailbroken, you have
many choices to lock your any applications and folders you want and I
personally recommend you to install the tweak called BioProtect for all devices
running iOS 7, 8 & 9.
BioProtect is
a jailbreak cydia tweak developed by Elias Limneos which allows you to protect
your apps and folders with Touch ID or Passcode. It is the most secure and yet
fastest way to protect your applications with a very cool UI. BioProtect adds
stylish protection to your applications and many other protectable items which
prevents opening them unless you authenticate using your fingerprint (Touch ID)
or entering a passcode(Device that don’t support Touch ID).
BioProtect is
available in Cydia via  BigBoss Repo for and is compatible with all devices
running iOS 7 or later. After installing this tweak, you can have many options
to configure from the settings app. Like you can congfigure it to protect
access to applications, folders, setting panes, flipswitch, control center
items, power down, SIM unlock and more. In addition to that, you can find
trusted wifi network, remember unlock session, and vibrate on error.
What’s new in
BioProtect:
Adds complete
support for Seng on the both iOS 8 and 9
Fixes an issue
that caused a crash on protected power down methods
Locks protected
applications from showing up in sliding-from-edge gestures

If you are still not jailbroken then follow this step by step guide on How to jailbreak iOS 9.0.2 using Pangu?