Before you can start using this plugin, it needs to be authorized against your Twitter account. This is because Twitter limits how frequently you are allowed to use their service, and connecting the plugin to your account protects you from other people over-using this plugin.
Click here and follow the instructions to authorize the plugin.
You can also choose to exclude retweets, and between monitoring the most recent tweets, or the most popular ones.
Here are some places you can look-up this ID:
Since the plugin will only return item titles in this mode, you will get best results if you turn on "Compact presentation" (in the Details tab of the channel's Properties dialog).