Understanding Customer Exit

Hello!

I want to understand, what i can do with a customer exit.

For example:

I have a simple wad-document with one inputfield,

one button and one customer exit item.

Is it possible, to write text in the inputfield and "export"

this text via the customer exit to "some kind of global variable",

so i can use this "global variable" in an other function or

webdynpro abap coding?

Know, what i mean?

Thanks

Chris