Grasshopper extensions determine how incoming calls are directed within your Grasshopper account. Callers will select an extension number based on what your main greeting says when they first call your Grasshopper number. What or who callers hear after they press an extension depends on how you set up your extensions.
At least one extension must be set up for you to receive calls, which is why all Grasshopper accounts have the default Extension 0. This ensures that you will start receiving calls right away.
Grasshopper has two different extension types: Department extensions and Employee extensions. There are no functionality differences between the two extension types. So you can use Department extensions for your employees and vice versa. The only difference is Department extensions use the numbers 1-6 and Employee extensions use 3-digit numbers starting with 7, so 700, 701, and 702 etc.
To set up your calls to ring directly to you without a main greeting, see How do I send calls directly to my phone without a greeting.
To set up your calls to forward to your extensions, see How do I set up call forwarding settings for my extensions.
For information on the usage of extensions with multiple Grasshopper numbers, see How do multiple Grasshopper numbers work on the same account.