How Do I French Braid My Hair?

A French braid is basically where the new hair is brought up over the usual braid.

First and foremost we will need to follow instructions by naming the area between the fingers. The first slot would be amid the thumb and the index finger. The second area is between the index and the middle fingers. The 3 slot would be the one between the middle and ring fingers. And the last one would be between the ring and the little fingers.

To start with you will first need to separate the part of hair from where you want to begin the braiding. Now hold the lock of hair in your left hand and push in your index and middle finger of your right hand all the way through the lock, starting right from below right to the surface, this in turn helps you separate the lock into three different strands. Now use you left hand to differentiate the strands out till the end of your hair. Now braid the hair the usual way.

Wow...it's easy to do, but difficult to explain!

You are really just braiding as usual:  Hair is separated into 3 strands, then the right strand is laid over the  center strand; then the left strand is laid over the [previously] right strand which is [now] the center strand, and so on.  The differences in the simplest form of french braiding are that
a) you don't separate ALL of your hair into 3 strands to start...ie: Comb the top part of your hair straight back; lift it up somewhat; now separate THIS hair into 3 strands and begin to braid it.
B) once you have braided this section of hair once (right over center, left over center) you are ready to begin to french braid:
Each time you are about to cross over the center strand, whether from the right or from the left, pick up some more hair from that side, and add it to the strand you are crossing with.  Continue your braid, adding to your strands as you go from side to side.  YOU ONLY HAVE 3 STRANDS THE ENTIRE TIME...they just get hair added to them as you go.
The tricks are:   How tight to braid;  keeping hair smooth when adding it to a strand; keeping strands smooth as more hair is added; keeping strands the same size as one another through out;

all of this comes with practice...i've been doing my own hair for years and i still pull it all out and start over some times!  
NOTE:  There is significant difference in french braiding your OWN hair, and french braiding SOMEONE ELSE'S.  In my experience, unless you're a professional, YOU CAN DO ONE OR THE OTHER...BUT NOT BOTH!  It's got to do with that mirror image thing...your fingers learn to do this 'upside-down' when braiding your own hair;  they are 'right side-up' when braiding someone else's...
One evening of trying over and over and over while you watch t.v. And you should have it down!!
I hope this helps!!

A hairdresser will help you with that