Some laptop and tablet computer manufacturers have a special adapter option to provide an Ethernet Connection (RJ-45 plug style) to the computer. Check with your computer manufacturer to determine the options that they might have available.
If your computer is a Desktop/Tower Computer, it may have available card expansion slots (often called PCI slots) where you can add an Ethernet Adapter Card to your computer.
There are also USB-to-Ethernet Adapters available: here are several examples. It is important to note that with those USB adapters, you may need to use a Standard Ethernet Cable, instead of a Crossover Cable.