Search Folders are different from rules. Rules move or take some other action on messages. Search Folders help you see messages without affecting them.
If you're familiar with rules, you may be wondering how Search Folders are different. The main difference is that rules perform some lasting action on a message, such as moving it from one location to another. For example, you might use a rule to move messages sent by a distribution list from your Inbox to a personal folder.
Search Folders are simpler (but certainly not any less useful). Their aim is to help you see different groupings of messages without changing their organization in any way. Rules organize; Search Folders leave that organization alone, unchanged. For example, if you wanted to see all the messages from your boss in one place, without moving them, you could use a Search Folder to do this.