In this step, we add a mechanical object with a mass and a solver to simulate our deformable body. See this tutorial
Add a new node to the root node. Rename the new node "Object".
Add an EulerImplicitSolver, CGLinearSolver, MechanicalObject and UniformMass component to the Object node.
We will add an internal force field, the PlaneForceField. It simulates a plane (direction + distance to the origin).
As a start, we will simulate a collision with a floor using this kind of "virtual object". In further steps, we will see how to use any real object as an obstacle.
A particle falls along the direction of the gravity, and remains on the plane defined by the PlaneForceField. Our dragon doesn't move. (Note: you may need to adjust the viewing angle in SOFA to see the plane. Make sure Collision is selected in the View tab in SOFA.)