Adam Bertram explains what hash tables are and why they’re useful:
Notice that each of the keys is unique. This is required in a hash table. It’s not possible to add two keys with the same name. Below I’ve defined the SomeKey2 key twice.
We’ve just talked about creating a hash table and adding key/value pairs at creation time. It’s also possible to add keys to an already created hash table in a number of different ways, either through dot notation, enclosing the key in brackets, or by using the Add() method. Each approach has the same effect.
Hash tables are quite useful in Powershell for storing key-value pairs, like if you’re building a dictionary of configuration settings.