PCLinuxOS is KDE.
1. If the sound works then you already have the correct driver loaded. For the graphics you have a choice: you will already be using the open source nv graphics driver, which is fine unless you want to play 3D games or do something else which involves 3D graphics. For normal 'serious' use, the nv driver is fine.
If you do want the fancy 3D graphics then you need to install the proprietary nVidia driver. I think that PCLinuxOS provides a fairly simple means of doing this, but it might be better to leave it for a later time when you're more familiar with how things work.
2. The Linux/KDE file manager is called Konqueror, and there is probably a launch icon for it on the taskbar - a little house very likely. By default, this will put you in your own home directory, where you can see your personal files. The icons on the left of the window give you different types of view on your system - I usually click on the little folder icon which makes the left hand pane into a tree view of the file system.
