A long long way from home

RJ45 alignment

To utilize these color codes correctly you should hold your RJ45 connector
with the locking thingy away from yourself, and with the little
metal contacts facing towards you.

Pairs

Most CAT5 cable comes with 4 pairs (otherwise, would it be a CAT5
cable?). On the standard, el-cheapo CAT5 from Biltema those pairs have certain color
codes. I use them as an example here.

PC to hub Cable

This is the most common cable, often referred to as a “patch cable”. One
end goes into your RJ45 compatible network interface, and the other one
fits smugly into your switch, HUB, broadband router or your least
favourite pets ass^H^H^H favourite toy.

Two computers over one CAT5?

Yes, this is indeed possible. Just remember that the plug utilizing pairs
3 and 4 should be plugged into the computer which transfers
the least data of the two.

This setup is most commonly used between a hub and a dual connector walljack.