How do I lock certain apps?

Select the yellow lock icon in the upper-right corner, then select the lock next to the apps you wish to passcode protect. Select the yellow lock whenever you want to enable or disable the app lock. Once apps are locked, only the passcode you created earlier will grant access.

Does Android have an AppLock?

Locking / Unlocking apps via All apps screen: From All Apps screen, tap > Lock apps. Input your PIN or pattern to unlock the AppLock feature. Tap the apps that you want to lock / unlock, then tap Done.