The upper jack accepts an RJ11 modular telephone connection. The red tab indicates a port connected to the LocalTalk network for use by older Macintoshes. The blue tab indicates a 10baseT Ethernet connection and is normally the port used by PC's. The cable used to connect your computer to the wall port is an Ethernet category 5 10baseT cable which typically has an RJ45 connector at each end. This is NOT the same as a telephone cable.
Network cables have eight pins, while telephone cables have four.
Cables are available from the Computer Store in lengths of six, fourteen and twenty five feet. In general, use the shortest cable that will reach comfortably from your PC to the wall port. You must provide this cable, although it need not come from the Computer Store. N etwork I nterface C ards are made by many manufacturers and come in a number of types. PC's may have any of five types of accessory slots, and a given PC may even contain two different types of slots.