9.1 Array indexing to use, modify or delete elements 

Indexing means "refer to the element position" in a vector or a matrix.
This video explains the concept to index one or several elements in a vector or a matrix. After indexing one or several elements, you can change them or delete them or use them in mathematical operations.
The video covers the following three topics:
A. Indexing & modifying one element
B. Indexing & modifying a range of elements (several elements)
C. Indexing & deleting one/a range of elements (several elements)