While the main camera is used for taking photos, videos and scans, the front camera is mostly used for "selfies" and/or facial recognition or for an iris scan to unlock the device (see biometric unlock).
Multiple front cameras
All current smartphones offer their users a camera, usually even several. A distinction has to be made between the main camera on the back (today usually multiple cameras) and the front camera on the user's front.
Front cameras are now also offered as multiple cameras (dual camera), which is helpful for creating a bokeh effect as well as controlling the depth of field.
Selfie flash
For brightening up selfies, some models switch the display to very bright for a short time (Apple calls this feature "Retina Flash"). This eliminates the need for a dedicated flash for the front camera.