When you send data through a hub it's forwarded to the entire LAN then read by the computer it's intended for. A switch sends data only to the computer it's addressed to, reducing network traffic and expanding capacity. Hubs can either send or receive data but can't do both at the same time. With a switch, a computer can simultaneously send and receive data, increasing the speed of the network. Switches used to be more expensive than hubs, but some kits now offer a switch at the same price as a hub.
Some cards can support multiple protocols or multiple media.
For example, you can get cards that have both RJ-45 and BNC ports for either twisted pair or thin coax cable. Some PCs come with NICs built-in but most require the addition of a card using either an ISA or PCI expansion slot. What you choose will be dictated by the type of expansion slots you have available. The PCI interface is more efficient, but older computers may not have free PCI slots. Laptops can use NICs that fit into the PC card slot.