Under the Apple menu on every Mac, the first item is “About this Mac,” which is a window into your hardware system.
Clicking it will bring up a new window:
This window has lot of goodies hidden away. For example, clicking the OS X version number will bring up the build number and your Mac’s serial number:
The More Info… button packs its own punch:
This window’s multiple tabs gives a high-level view of your Mac, including information about displays, RAM, and storage. For example, here’s the current state of the 512GB SSD inside my own MacBook Air:
Like a gift that keeps on giving, however, About this Mac has one more layer, hidden behind the System Report button.
This app — named System Information — is one of the oldest parts of OS X. It’s been around forever, and is the best place to get down to the nitty gritty details of your system:
As this Macworld article points out, System Information is a treasure chest of helpful information, and is well worth the time exploring.