If you mean a standard 10/100 type Network Interface Card (nic), then you connect it with a CAT5 or CAT6 cable, the connector on the end is known as an RJ45.
The type of connector is used by the analog modems is RJ11 or RJ45.
Nowadays, a discrete GPU needs a PCI Express x16 slot.
PCI , AGP and PCI Express
Yes. An air card is essentially a modem with a cellular phone built-in.