10/100 is speed in megabits per second. eight bits is one byte. So 10mbps is 1.28MB/s (megabytes per second) - in theory. Real world factors mean that it's often lower.
Of course that speed would only be between computers on your home network. Your internet speed is determined by the distance from your exchange, your ISP and plan you have with them.
Technically, it's 10M OR 100M. It means it can connect to a machine with a 10M port or a machine with a 10/100M port. Likewise a machine with a 10/100/1000M port can connect to machines with a 10M, 10/100M or 10/100/1000M port. The ethernet controller will automatically switch speeds to adapt to the speed of the port it's communicating with.