Step 1

1.) Open the Blender and delete default cube.

Step 2

2.) Add or create any mesh you want.

Step 3

3.) After you are content with your creation, go to edit mode and press x and then delete only faces.

Step 4

4.) Then, select File => Export => Wavefront (.obj)

Step 5

5.) Save file with only following options: Include Edges, Keep Vertex Order