Open Autodesk Inventor
Create a new part file
Start a 2D sketch on the XY plane
Draw the top profile of the bike seat
Draw the side profile of the bike seat
Add dimensions to define the seat size
Add constraints to fully define the sketch
Finish the sketch
Use the Extrude tool to create the main seat body
Create a second sketch on a side or top plane
Draw the seat curvature or contour
Use the Loft tool or Cut Extrude to shape the seat
Add fillets to round the edges
Create a sketch for the mounting rail or base
Extrude the rail or base geometry
Add holes for mounting hardware if needed
Use the Mirror tool to copy symmetrical features
Apply additional fillets and chamfers
Check the model dimensions
Save the part file
Create an assembly file if you want to add the seat to a bike model
Insert the seat part into the assembly
Constrain the seat to the bike frame or seat post