Gmail's filters allow you to manage the flow of incoming messages. Using filters, you can automatically label, archive, delete, star, or forward your mail, even keep it out of Spam -- all based on a combination of keywords, sender, recipients, and more.
To create a filter:

1. Click Create a filter (next to the Search the Web button at the top of any Gmail page).
2. Enter your filter criteria in the appropriate field(s).
3. Click Test Search to see which messages currently in Gmail match your filter terms. You can update your criteria and run another test search, or click Next Step.
4. Select one or more actions from the list. These actions will be applied to messages matching your filter criteria in the order in which the actions are listed -- for example, you could choose to Forward matching messages to a specific email address, then Delete the messages. Note that if you choose to forward messages to another address, you'll need to first verify that you own any new forwarding addresses.
5. If you'd like to apply this filter to messages already in Gmail, select the Also apply filter to x conversations below checkbox.
6. Click Create Filter.

Please note: When you create a filter to forward messages, only new messages will be affected. Any existing messages that the filter applies to will not be forwarded.
To create a filter from within a message:

1. Click the drop-down menu next to Reply.
2. Select Filter messages like this.
3. Enter your filter criteria in the appropriate field(s).

To edit or delete existing filters:

1. Click the gear icon in the upper-right and select Gmail settings (at the top-right of any Gmail page).
2. Click Filters.
3. Find the filter you'd like to change and click its edit link, or click delete to remove the filter.
4. If you're editing the filter, enter the updated criteria for the filter in the appropriate fields, and click Next Step.
5. Update any actions and click Update Filter.

You can create an unlimited number of filters, but only 20 filters can forward to other addresses. You can maximize your filtered forwarding by combine filters that send to the same address.