In order to connect a computer to an Ethernet cable, the computer must have an interface. In a desktop this is usually a Network Interface Card (NIC) or USB adapter. In a laptop, it is usually a PC card, a module that plugs into the laptop. The Ethernet jack may also be built into the laptop itself.
You can make a very simple network if you have an interface in each computer and an Ethernet cable.
In order to connect a computer to an Ethernet cable, the computer must have an interface. In a desktop this is usually a Network Interface Card (NIC) or USB adapter. In a laptop, it is usually a PC card, a module that plugs into the laptop. The Ethernet jack may also be built into the laptop itself. 
How do I connect computers?