ok, so the ENTIRE site needs a host and then you edit the site on-line. You also have access to all the code.
you can download wamp/xampp and install silverstripe locally and develop locally. But the whole site (everything you download from silverstirpe.org and your database) needs to be be uploaded when you want peo0ple to see it ont he internet
Silverstripe *does not* host the site - there are some place that offer a dedicated silverstripe hosting. I have used several different hosts and each can have slightly different issues to get it installed and running (which is why I pointed you to the suggested hosts). silverstripe give all this away for free - they don't provide hosting free as well!
I doubt "free" webspace is gonna work out because you'll probably want a mysql database - if you find a free host, no ads with a mysql db - tell me where it is!
You might get away with using the sqlite module to use the "stand alone zero-configuration" database but in order to get staqrted I'd stick with mysql