Indexing means to refer to any value in an array. Each item in a numpy array is stored at a specific index. To access value at a specific index write:

Z=np.arrange(9)
Z[0] #get the value at index 0

Get the First Value

To get the first value of a matrix, write: Z[0,0].

   ┏━━━┓───┬───┐   ┏━━━┓
   ┃ 0 ┃ 1 │ 2 │ → ┃ 0 ┃ (scalar)
   ┗━━━┛───┼───┤   ┗━━━┛
Z  │ 3 │ 4 │ 5 │  
   ├───┼───┼───┤
   │ 6 │ 7 │ 8 │
   └───┴───┴───┘