Message filters can be added in Thunderbird to filter incoming emails to a different folder.  This can be used to divert spam to the trash, or to re-direct some important emails straight to a certain folder such as receipts or business related information.  To create a message filter in Thunderbird, first under the "Tools" toolbar option select "Message Filters:"

This will pull up the Message Filters popup window:

To make a new filter, select "New..." on the right hand side, which will pull up a new window where you can put in your filter:

Once you have added the information you want to filter as well as the folder that you want the message to filter to, click "OK." Now on the Message Filters screen you will see the filter that you just created:

You can create as many filters as you need to for your email account.  If you have created a filter and want the filter to be run on messages you already received (and are still in the inbox) you can click the Run Now button at the bottom of the Message Filter window.  This will "run" the filter on messages you have received and place the email messages in the folder specified by the filter.