We give part of the shape of the feet with the help of Edge Loops (yeah, more... sorry) and Proportional Editing (activated with O key) which give you the power of take a single vertice or face or edge and make all the near ones get affected.
Here is the latest render (the one for this tutorial):
A little breakdown for the video:
- Extrusion for the bottom part of the leg to start shaping the foot part.
- Addition of edge loops at that bottom part.
- Selection of the bottom face and Proportional editting enabling (O key).
- Extrusion (inner extrusion) of the side faces of the foot to place the wheel.
- Deletion of some faces from foot to let the wheel to be seen.
- We use the Knife tool (K key) to create additional faces in the foot.
Here you have the video:
If you want the .blend file you can download if from the following link: