Just click on the object, in this case the dinosaur's head, and start connecting the dots. You should see orange lines that make the object's wire frame, just like in the image (Fig.08).
In the process of retopologizing your mesh you should go into Preview mode every now and then to check the mesh for consistency and make sure everything is OK. You do that by pressing the Preview button under the Adaptive Skin palette that is located a couple of options above Topology, or you can simply press A on the keyboard. In Preview mode your mesh should look something like this (Fig.09).
As soon as you complete the entire object and you are happy with the result, the mesh should be turned into a polymesh by clicking the Make Polymesh3D button positioned at the top of the Tool menu (Fig.10). Now you are ready to either project details from the messy old mesh, or, if you don't have any details, start detailing the clean mesh.
For detailing this dinosaur I used a couple of custom-made alpha brushes that I created specifically for this occasion, which can be downloaded here
. The method I used to create the custom alphas is nothing special really. I selected a Plane3D object from the Tool palette, under the main Tool menu (Fig.11). I turned it into a Polymesh3D and subdivided about six or seven times to extract the alpha brush as smoothly as possible.