This video tutorial will help you specially the beginner to know how splines
use in interior and external furniture designing. First of every one check that your chair has right dimensional. Always start the modeling in top view, for chair modeling, take four-sided figure in a top view and zoom in. click anywhere in the view port and you will see that there will be rectangle in modifier option.
Right click on rectangle and then click on rectangle spline. In modifier there will be section option select that option. Press one segment and with key select the other segment as well. Another option split will help you in creating more vertices. Just right click on the object and there will be option of bend select that mode. Now select go tool and give them shape as much you necessary. When you will see in prospective view this will be in solid rectangular shape.
With help of filet authority you can set the vertices and edges. Now sketch a line for back and seat and enable the render and view port. Select its vertex and use filet command to give them round shape. You can see the round shape by doing zoom. For seat, extrude the modifier as of modifier list and adjust it as much you want. It will be last result.