A 'PPT' file is a Microsoft Powerpoint document. You can open them with PowerPoint for Mac, OpenOffice (and derivatives NeoOffice, LibreOffice, and Oracle Office), Apple Keynote, and Google Docs.
Open Office can be downloaded from OpenOffice.org and it is free.
Google Docs is web-based office suite. While it's a little awkward, it will permit you to import PPT presentations.
Most of them do a good job, but each will fall down with certain types of content. If the presentation contains ActiveX controls, they won't work on the Mac. Macros won't tend to work in anything but PowerPoint itself. Your mileage will vary on audio/video and embedded web content. There are also differences in transitions and animation between products that give peculiar results when going from one to the other.
If the presentation is a fairly typical one, however, all of the above will do a fair job of displaying it.
Okay so I downloaded openoffice and everything was great, until I got to a section with sound and seems I cannot hear anything. Any help much appreciated.
Remember that is free software, you probably should invest in MS Office 2011. It's not too expensive, you can get a license for about $120 from Amazon. This would include MS Word, MS Excel and PowerPoint.
One other possibility is purchasing iWork. iWork has Pages, Numbers and Keynote. Each of those applications will open their MS Office equivalents and you can get that for less than $70.
What kind of sound? One thing that you will see is that Windows users will tend to use Windows-proprietary media types very often. If they used an MP3, you can here it. But if they use WMA, you won't be able to hear anything unless you have Flip4Mac installed.
