Hi Ester,
To install the module, you will need to drop the folder inside the zipped file into the silverstripe directory on your web server (where all your silverstripe files are hosted).
are you with a hosting company? some hosting companies have a web portal you can log in to (cpanel for instance), from there you can get access to the files on the web server and upload your own.
Personally to make things easier, I would use an ftp client. Smartftp is a fantastic ftp client, but feel free to use whatever you like.
once the googleanalytics folder has been uploaded to the root of your silverstripe directory on the web server you will need to rebuild your database.
To do this you just need to use {website}/dev/build?flush=1 (where "{website}" is your web address).
All of the above assumes you know the login details for your web server.
Thanks,
-helenclarko
P.S. I dont believe the GoogleAnalytics module works with SilverStripe 3.0+ as of this time, you may need to set it up manually.