It would be easier if you'd point out what you don't understand about it...

Well, pointers only represent the physical memory adress of the data they are referring to. So whatever kind of data you have (strings or large structs) the corresponding pointer will always have four bytes.
This can be extremely useful if you want to create a fast sort routine because you'd only sort pointers instead of huge amounts of data.
Also you might want to pass variables to functions in order to process them - with a pointer you hand over the adress and that's it.

On the other hand you have to be careful not to use pointers that point to the nirvana - an access violation will be the consequence.