Accelerated Graphics Port:
The Accelerated Graphics Port (AGP) is the part of your motherboard which allows the user to connect video cards to a computer system. This is a dedicated point to point channel port specifically for video cards allowing higher quality video cards to be used in the computer system.
This is the specialised card for your computer that allows you to be able to connect the given computer system to a network, this is more often than not done through an ethernet port which allows you to connect to your router giving you internet access. However nowadays most modern computer systems have wireless internet access without having an external network card, (assuming that the card is inbuilt into the motherboard).
This is the card that is responsible for the high quality output on your computers output display. This is a card that can be built into the motherboard of the computer system or can be externally added to the motherboard of the computer to produce an even higher quality output from the computer onto the connected display(s).
A modem card (more commonly known as a 'PC Card' is used in computer systems to allow for telecommunications within the computer system.
To be able to have sound output from your computer you need a sound card for your computer to be able to have a sampling rate ergo having sound output. Sound cards can either be built into the computers motherboard or can be externally added to the motherboard of the computer whenever.
The quality of the sound card installed on the computer would depend on the sampling rate of the sound card at hand.