Living in Sweden, I could not log in and activate Google Music. After a little googling I came across a very simple way of using Google Music outside the US. You need to make the Google Music web site think that you are in the US, and the awesome thing is that you only need to do this once when you activate the service.
To activate Google Music outside the US, follow these simple steps:
1. Go to browsertunnel.com
2. On that page, in the address text field, enter https://music.google.com
3. Log in and accept the agreement
4. Download the Google Music uploader tool and start uploading your music!
If you have an Android phone, you might want to downoad the Google Music app. Google, the search engine, can help you find it ;) (it may be as simple as installing it from Android Market)
However, the Google Music app was already installed on my phone, which is a Samsung Galaxy Nexus.