Hi Tornike,
the numbers your are asking are the number of neurons on each of those layers.
for kernel_initializer (docs 3), this defines how the starting random weights of that layer will be initialized. the ‘normal’ might (I don’t know for sure) generate the numbers from a random values from a Normal distribution.
y.shape[1]  is the second dimension size of y, for example:
a = [[1, 2, 3],[1, 2, 3]]
b = tf.constant(a)
b.shape
>>> TensorShape([2, 3])
b.shape[1]
>>> 3

you can find more information here: tf.shape  |  TensorFlow Core v2.5.0 1