Problem with Piwik in Magento 1.9.1

After installation piwik in magento 1.9.1 in the backend I have this message "You are missing your Piwik Token Auth Key. Get it from your API tab in your Piwik Install."
How to solve this problem ?

Go in your Piwik install, login and go into your account settings (click on your username on the top right).

In your account settings there is a “API” tab, and here you should be able to get your API token key.

Where is my Piwik install ? In Magento do not know where I can find my instal piwik.
Thank you for your help.

OK you need to read the guide from the Magento plugin. It probably says at some point that you have to install Piwik.