Choose the Home tab→Sketch group→Sketch command 
.
Select a reference plane.
A sketch view is displayed and sketch commands are displayed.
Use the sketch commands to draw the 2D geometry you want.
When you are done drawing in the sketch view, choose the Home tab→Close group→Close Sketch command. You can also click the green check box 
in the upper left portion of the sketch view.
The model view window is displayed.
(Optional) You can assign a name to the sketch by typing it in the Name box on the Sketch command bar.
When you are finished with all work in the sketch, on the command bar, click the Finish button, and then click Cancel.
Tip:
You can modify the sketch in two ways:
Before you click Finish, you can click the Draw Sketch Step group button on the Sketch command bar to return to the sketch view window.
If you have already clicked Finish and exited the sketch, you can right-click the sketch name in PathFinder, and then choose Edit Profile or Edit Definition from the shortcut menu.
You can use the sketches to construct features. If you edit the sketch, the features will update.