Start by opening any Excel document (blank or otherwise). If you navigate to the Insert ribbon, there will be a get add-ins option you can click:
In the window that pops up, search the “store” for “Amalgam” and click Add on the result you find. After selecting “continue” on the privacy policy, the plugin will be added to your home ribbon.
To open the plugin, simply select the button at any time from the ribbon to launch the sidebar.