Avoiding white when exporting

Hi, everyone,

I'm teaching myself Illustrator by replicating some logos. I just tried the FanDuel logo, which is similar to a blue shield with a white slash through it. I drew a blue triangle and then a white curved line over it that makes the "F," and it looked good against the white background. But when I exported it as a .png...duh, there's a white line over the logo instead of an absence.

Suggestions? Thanks!