WordPress.org

1. Download the plugin
2. Unzip momentile-on-wordpress.zip
3. Upload the entire momentile-on-wordpress folder to your plugins directory
4. Go to the Plugins page in your WordPress Administration area and click to 'Activate' Momentile on WordPress.

Then either:

1. Add your Momentile username on the settings page, and change any other settings as required
2. Go to Appearance->widgets and add the Momentile on WordPress widget to your sidebar

or:

1. Open your theme folder
2. Open sidebar.php in a text editor
3. Add into the code where you want the widget to be (image width and image shape default to '64' and 'square' respectively).