How extend method is different from append method in Python?

Suppose I have two lists, one containing customer name and other containing product name.

Customer = [ ‘Harry’, ‘Aisha’, ‘Neha’, ‘Ahmed’]
Product = [ ‘Shoe’, ‘Brush’, ‘Pen’, ‘Laptop’, ‘Noodles’]

I have learnt two methods of list, append and extend. As both are used to add items.

Customer.append(‘Kareem’)
Product.extend(‘Book’)

Both are working fine. Why do we need two different methods for adding items to a list? Are these methods the same? What key feature creates the difference between these two?