Text-to-speech (TTS) technology enables software and applications to play back written text as human spoken words. You can use PowerPoint 2010 and other versions of powerpoint to speech every time you highlight a text on the screen or slide. In other words, you can hear most text that appears on your screen in Word, Outlook, powerpoint, OneNote and Microsoft Office programs.
To enable text-to-speech in powerpoint 2010 you can add the command to the Quick Access toolbar. Right click on the top of the Quick Access toolbar to configure it.
Then, you will see Quick Access Toolbar options and chosee All Commands from the top list. Then look for Speak command and add it to the right select list. This is the list of active Quick Access Toolbar commands.
You can also use text-to-speech in different languages, but for this purpose you will need to enable the Multilingual TTS.
If you are looking how to use TTS to automatically speak while presenting a Slideshow or powerpoint presentation, you can learn more about PowerTalk, it is a free tool that you can use to make your powerpoint presentations speak.