Open SolidWorks
Create a new part
Select the Front Plane, Top Plane, or Right Plane
Start a Sketch
Draw the seat outline using lines, arcs, or splines
Add dimensions and relations to fully define the sketch
Exit the sketch
Use Extruded Boss/Base to create the seat thickness
Create the seat back by sketching on a side plane or face
Extrude or loft the backrest shape
Use Fillet to round sharp edges
Use Shell if a hollow structure is needed
Add support legs or frame members with sketches and extrusions
Mirror components if the design is symmetrical
Apply additional fillets or chamfers as needed
Save the part
Create an assembly if multiple seat components are required
Insert the seat part into the assembly
Mate the components together
Apply materials and appearances if needed