After you install the module and open it, the first screen will enable you to clean the Cache on your XOOPS Website. This is just an extra benefit of this tool.
The actual Block Manager is on the second tab.
Here you can review and modify your your existing blocks
On the second tab you can add new blacks that you want to manage. The Block Tools will show you all existing blocks for all modules, and you can select those that you want to manage yourself.
The third tab is for editing your existing modules.