Tiffano,
You have not specified what card you want inserted. Anyway.

Please remove the 3 screws at the back of the PC on the right side of the PC as you face to back. This will enable you to remove the cover thus exposing the innards of the PC. You will find at least one slot empty for a cord to be inserted. Insert the card with its contact lugs towards the motherboard and the metallic strip towards the back.. Fit it properly and tighten the screw on top of the metallic strip to the body of the computer. Once done, screwup the side plate of the PC and turn it around to face you. Now insert the CD that came with the card and install the card.
Now you are ready to use the card.