copy- what's my root directory?

I've got another newbie question.  I want to copy some csv data into my postgresql database.  I'm confused with the syntax though.  I entered

mydb=# copy mytable from '/data.csv';

It tells me it can't find data.csv, which means I saved it in the wrong place.  I've tried the data and scripts folder.  Where do I save import/export files and where is all my database work being saved?

Thanks.

Eric