Hello and welcome to LinuxQuestions,
First of all you'll have to learn how to ask a question (see link in my signature); next you at least have to try to find something for your own by using a search engine like Google, which would have given you this
. Are you referring to connecting to a LAN? WAN? The Internet? Cable connection? Wireless? Is your network card connected and detected by Ubuntu? And so on...
If the above result in errors, then post them here, being as complete as possible and providing as much information as possible.