Firstly the case of the computer needs to be opened and this should be done when the power is off. Make sure you have an antistatic wrist strap that is attached to your wrist so you can be grounded while working on the Pc.
Step two, take the network card and install it into one of the PCI slots by aligning the guide notches with the PCI slots.
Step 3, press straight down on the network card with gentle pressure until the card fits completely onto the PCI slot.
(The network card is the green card in the image above)
Step 4, secure the network card with a single screw so that it can be attached to the Pc.