Working with differnt types of solidworks sketch!

Working with different types of Solidowrks sketches, there are three types of sketch we deal in Solidworks.
Types 1: Open sketch is that in which entities never make a closed loop.
Type 2: Closed sketch is that which has ne closed loop.
Type 3: Nested sketch has more than one closed loops.

We can use Solidworks Thin extrude with open sketch.
Normal extrude with closed sketch.
And use Sketch contours with nested sketch.