Adobe animate need help !!

So i recently dowloaded adobe animate 

And ive had a major problem:

So when i upload a sketch ive created on a different program onto adobe and start my work on it

1st of all: lines i create dont go under a symbol and when i use the square symbol for background it also doesnt go under symbols. They all go behind my sketch upload. Or the remain on top of the symbols

Ive tried going on arrange and bring forward, backward, Nothing works what do i do