One of the more controversial aspects of Windows 8 is that the Start button has disappeared altogether -- a conscious choice by Microsoft to encourage people to adopt and use the Metro interface. There's not much chance of it officially returning, but there is a minor replacement of sorts built into Windows 8.
With most of the code that generated the old Start menu deliberately stripped from Windows 8, third-party developers are going to have more work to do to migrate replacements (such as my own favourite Classic Shell) to the new platform. In the meantime, the nearest equivalent is the 'advanced context menu', a simple grey list of options which appears in the same area of the screen as the old Start menu.
You can access this by hovering in the bottom left corner on the desktop and right-clicking on the shrunken Start screen or desktop image, or my easily by typing Windows-X. From here, you can access a bunch of system-level features (such as Device Manager and Power Options), as well as load a command prompt or the Run command, access Explorer and perform searches. Many of those features can also be accessed via keyboard shortcuts, but it's handy to have them in one place if you don't have the shortcuts memorised.
This doesn't directly fix my own personal preferred use of the Start menu as a means of quickly launching applications with the Windows key followed by a single letter. You can partially customise what appears on the list, but it's a really fiddly process and I'm not going to consider it unless it becomes clear there won't be other alternative launchers available.
However, if you've been used to the Start menu as a way to access the Control Panel or other options, this is a reasonable fill-in of sorts.