How do you dial an extension number?

In most cases, you first dial the main number. If an automated system answers, you will be prompted to dial the extension number.

For example, to reach (318) 555-0123 x 7838, you would first dial 1-318-555-0123, and then, after the automated system answers, dial the extension number 7838. If a human operator answers, you can just say, "Extension 7838, please."