In Forma, from the list of your proposals in the left-side panel, left-click on the 3-dot menu of the proposal you'd like to work on and choose “Send to Revit” from the menu.

Open Revit and create a new project. In the Massing and Site tab, find the Load Proposal button. (Note, if you are loading a Forma proposal into an existing Revit project, the existing Revit location data will be overwritten by the GIS coordinate system used to locate the Forma project)

Note: while the add-in is regularly being improved, current conversions are 

• Basic Buildings and Released Line Buildings are converted to Walls, Floors, and Roofs
• 3D Sketch Buildings are converted to loaded mass families with mass floors
• Line Buildings, Vegetation, context buildings, and ShapeDiver elements are Converted to Generic Models (Direct Shapes)
• Parking is converted to Parking Components (Testfit parking is currently not supported)
• Terrain is converted to Toposolids in Revit 2024 (toposurface in previous versions)

For more details, see the Forma Revit Interoperability documentation.

Installation

Run the included Windows Installer .msi installer.

Uninstallation

Windows Start > Settings > Apps and Features, search for Forma, select Forma Revit Add-In, and click Uninstall.