Dolores...What type fence are you building....wood, vinyl, chainlink, etc?
You will need posts set into concrete at intervals. Then add rails and vertical pieces. Another hint a concrete strip under the fence or a non-grass area will keep grass away the fence. That will eliminate lots of trimming and wasted time each week.
Here is a article on building a fence https://www.homedepot.com/c/ah/how-to-build-a-fence/9ba683603be9fa5395fab90a485b4ce