There are at least five ways to put your Mac to sleep. In decreasing order of how much time they take, they are:
- Choose Sleep from the Apple menu
- Hit Control-Eject and then S (or click the Sleep button in the dialog that pops up)
- Press the power button (for desktop Macs)
- Close the lid (for laptops)
The fifth method is to hit command-option-eject. Note that all of these will also lock the computer if you have it set up to require a password after the screen saver kicks in.