imported .stl model is tiny. How can I set the scale correctly? I am importing .stl to blender. Once it was imported, the object appeared in blender as a tiny dot at the center of the grid(0,0,0) 
For example, when I created an object with the dimension of 1.18cm X 2.99cm X 3.19cm, then export it to .stl. Later on, I import it to blender, the dimension became 
1.18m X 2.99m X 3.19m. Why does blender change cm to m? is there something I am not setting correctly in Blender?
STL file does not have information about units and their scale, https://en.wikipedia.org/wiki/STL_(file_format)  

So you need to set the units and scale in Blender before importing your stl. This is done on "Scene" tab under "Units" group.