How does numpy.newaxis work and when to use it?

When I try

numpy.newaxis

the result gives me a 2-d plot frame with x-axis from 0 to 1. However, when I try using numpy.newaxis to slice a vector,

vector[0:4,]
[ 0.04965172  0.04979645  0.04994022  0.05008303]
vector[:, np.newaxis][0:4,]
[[ 0.04965172]
[ 0.04979645]
[ 0.04994022]
[ 0.05008303]]

Is it the same thing except that it changes a row vector to a column vector?

Generally, what is the use of numpy.newaxis, and in which circumstances should we use it?