1) Decide if you want to model this with beam elements, shell elements or solid elements. Create Geometry in SpaceClaim for the Length and cross-section of the beam. Draw only half the length to use symmetry at the center.
2) In Mechanical, create a Symmetry Region at the center and select the geometry at the center. Make sure to set the Direction normal to the plane.
3) Create a Translational Joint at the other end to compress the beam.
4) Add a tiny side force to the geometry at the center to seed the deformation.
5) Add a Joint load, type=Displacement. Type in a number that is 2% of the length.
6) Under Analysis Settings, turn on Auto Time Stepping. Make the Initial, Minimum substeps 100 and the Maximum substeps 200 and turn on Large Deflection.