You can get a trial version of Rhino3d and Grasshopper from the Rhino3d website. Run Rhinoceros and select the template with Meters:
In the Command line, please enter "Package Manager":
A new window appears; select IDEAStatiCa and click Install. The plugin will be downloaded and installed. To become active, a restart of Rhinoceros is necessary.
To start Grasshopper with the IDEA StatiCa plugin, select Tools / Grasshopper in the Rhihoceros tab.
As you can see, the plugin is already incorporated.