Let's dive into how we can work with Redis sets using PHP. Redis, as a versatile key-value store, supports various data structures, including sets, which are collections of unique, unordered elements. In this lesson, we'll look at how to add and retrieve items from sets with PHP.

First things first, let's connect to your Redis server and add some items to a set:

• We use the Predis library, a PHP client library for Redis.
• We establish a connection to the Redis server via the Client object.
• With the sadd command, we add items to a set called countries. The set nature of Redis automatically ensures that no duplicate entries exist.
• Using the smembers command, we retrieve all members and print them. Despite adding "USA" twice, duplicates are not stored.

Now, let's look into how to find out the number of items in a set and remove a certain item.

• We determine the number of items in the set using the scard command, which tells us how many unique items are stored.
• We then use the srem command to remove the specified item from the set — in this case, "UK".
• After removal, we can confirm the operation by re-checking the set's current items.

In this lesson, we delved into the use of Redis sets in conjunction with PHP through the Predis library. We learned about the fundamental properties of Redis sets, which are collections of unique, unordered elements. This ensures that no duplicate entries exist within a set. By interacting with Redis sets, we enhanced our understanding of how to add, manage, and retrieve unique data efficiently. Additionally, we examined how to assess the size of a set to understand the count of unique items it contains, and how to remove specific elements, thus demonstrating the versatility and utility of Redis sets in managing collections of distinct data elements within a Redis data structure.

Keep these operations in mind as you start experimenting with your own applications. Happy coding!