What is casing drilling?how many types of ?what are the advantages of casing drilling?

Casing is a tube (pipe) inserted in the borehole. It follows directly after cementing.There are mainly five types with different functions as follows:

1) Conductor

2) surface 

2) intermediate

4) production

5) liner  

Each casing type have different advantages but mainly casing is supporting the wellbore from collapsing.