Simple Question about Hooks & Plugin development

Hi,
im new to wp and want to learn how to write plugins. Im a quite experienced php programmer so i only have to learn about the wp api.

I have a simple question:
If I eg. simply want to add a <div> – Container with dynamic Content (generated by php code) to the whole Blog (should be display with float:right on every Page).

so i got the function generateDiv(), but how and to what should i hook this function?

Thx 4 help