Setup a wordpress.org site but can't work out path to files

I’ve setup a wordpress.org site on a new domain/hosting and imported the files from the old wordpress.com installation – and that all works fine.

If I FTP onto the site I can’t see many files and the few that are there don’t seem to be enough – are they hidden? is there a way to un-hide them? (I’m using FileZilla).

Also, if I FTP an image into the site to the root directory (or any directory) I can’t work out the path for it (I need the URL to use it in a plugin). PMI, I’m a web designer but new to WordPress and a bit baffled by it.