No Preparation – Here is a hole feature with no preparation:

 

Countersink – Specifies a tapered preparation hole. Countersink has an included angle of 45 degrees. You can only define the countersink using either Depth or Diameter. Here is a hole feature prepared with a countersink:

 

Counterbore – Specifies a fixed diameter preparation hole. Here is a hole feature prepared with a counterbore: