how can I transfer ppt folders from my pc to my ipad?

You first need an app on your iPad that supports powerpoint files so that you have somewhere to copy them to - an iPad doesn't have a file system like a normal computer, everything has to be stored in an app. The options include Apple's Keynote, and from third-parties apps such as Documents To Go ('premium' version if you want to be able to edit them) and QuickOffice Pro HD. As to how you then get your powerpoint files into the app will depend upon what the app that you chose supports e.g. via the file sharing section at the bottom of the device's apps tab when connected to iTunes, via your wifi network, email, dropbox etc.

As King_Penguin said, you'll need an app for that.

There are more, but I found Presentation Note to be the best fit for me. With it, you can transfer PowerPoints and PDFs from your PC/Mac or even import from DropBox and similar services, and present directly from the iPad with really useful in app tools. You can even control the app with your iPhone with a companion app called Presentation Note Remote. here is a link to the free version: http://bit.ly/UnI7Mb

The other apps that were mentioned let you edit presentations - this one's optimized for presenting.