If you have a Mac you can enable internet sharing from an ethernet connection to WiFi
System Preferences -> Sharing -> Intenet Sharing -> Ethernet to WiFi
However, this is a bit rude and crude, and I would only suggest it until you follow Illaass' advice and get a WiFi router.
If you have a Windows system, I do not know what built-in or add-on software is available to share the ethernet connection via WiFi. Some Google searches will most likely turn up something.