The typedef is to shorten the naming of some types e.g. is you want to have short unsigned called SHORTUN for quicker typing you can use the type definition syntax of
typedef
so regarding the example of short unsigned to SHORTUN
typedef short unsigned SHORTUN
a probably better example would be if you wanted to have a apple as a type (which would be a integer value) then you could
typedef in APPLE
now you could use the code
APPLE apple = 1;