Layers question

I'm a little new to this aspect of web design...could someone tell me what
it is I need to do to get items to display on top of one another (via
layers)? Even when I assign high z-indices to an id, it still interrupts
the flow of the page. I need it to not interrupt the flow (like it's
display is "none"), yet be visible and cover another part of the page. What
am I doing wrong?

tia,
Aaron