a = np.array([1, 2, 3, 4, 5, 6, 7, 8])

e = a[1:8:2]



as a reminder.
The first element is: a[0]<-- index=0
a[0]=1
The second element is: a[1]<--  index=1
a[1]=2
The third element is: a[2]<--  index=2
a[2]=3
The fourth element is: a[3]<--  index=3
a[3]=4
The fifth element is: a[4]<--  index=4
a[4]=5
The sixth element is: a[5]<--  index=5
a[5]=6
The seventh element is: a[6]<--  index=6
a[6]=7
The eighth element is: a[7]<--  index=7
a[7]=8
now

e = a[1:7:2]

will create an array e that will have the start element with index 1 to the last element index 7 (not included) with an increment of two.

([2, 4, 6])