Wide screen question

Hi all,

Im trying to set mu After Effect project for a PAL wide screen,

It seems that my setting need to be 720x576 but my question is…

720x576 is somethink a cube shape, not a wide rectangle…saying wide screen I imagine somethink like 720 x 320 or something like that?

How it works?
If i do all my progect in 720x576 how it can be seen as wide screen?