|Is this a desktop?|
If your computer has USB ports--which it does if it was built within the last 15 years or so--then the ports are in the back in the back panel area near where the mouse and keyboard plug in. Most have additional ports in the front panel.
If you've bought a PCI USB card and need to install it, well you open the case and locate an empty PCI slot. With a phillips screwdriver remove the screw that holds the plate that covers the opening for that slot. Put the PCI card in the slot and put the screw back in so it holds the card in place. DO ALL THIS WITH THE POWER CORD REMOVED. Then start up the computer. If it's a USB 2.0 card you'll probably need to install drivers.
If it's a laptop, well, the USB ports are there somewhere. You may need to consult the manual for your particular model.