edit online WP

totaly new to WP, I just registered online, got a user name and a username.wordpress page, to play and see if I want to install it.

can I edit layout and images when using wp in online only mode (not installed on my server) or is it limited to posting text?

do I have to have my own space on a server somewhere in order to load any files to an online wp blog? can I change the img behind the header for instance?

how can I tell what version number wp I am working on if I have not installed it? is the blog located on a word press server?

thank you