The M7 has only a rear camera, no front camera, so you can't install a front camera. (A camera is a part of the inside of the tablet - you'd have to redesign the motherboard to accept a front camera, then make a hole in the front of the tablet to let the camera see out of the case.)
As for a camera app, just install it the same way you'd install any app.
What "better" are you looking for? The camera is 2MP - it's not going to be very good. (You can't expect much more for Rs900.)