Blender is useful to fill or mend a hole in a mesh. Holes are typically already present in a mesh or you create them while deleting elements of a mesh.
Edit Mode and then click the
Vertex select mode button. You are now ready to select vertices.
Select the vertices that border the hole. To do this, keep the
Shift key pressed down while you select the vertices by using the right mouse button.
f key to fill the hole. Blender tries to fill the hole with a suitable polygon. If you want to fill with triangles, then repeat these steps for every 3 vertices that form those triangles.
Tried with: Blender 2.62 and Ubuntu 12.04 LTS