role of Controls and relation with Program

Hi!

could anyone explain me what is the role of Controls and a program?

For example, for creation of Invoice and Invoice List is used the same program - SAPMV60A, but different controls: TCTRL_UEB_FAKT for Invoice and TCTRL_UEB_RELI for Invoice List.

What is the role of these controls?

Will reward,

Mindaugas.