Start by filling out your profile. You will have access to different projects depending on your devices. Remember that a project may be geared to testing with a specific device, and if you have not registered it in your profile you will not be able to access.
To raise your level and win as many badges and points as possible on the way you have to follow the Good Beta Tester guide.
How do I earn points?
These are the different ways you can accumulate points:
Testing. Points will be awarded according to the test complexity as defined by the Project Manager (simple, average, complicated). The more difficult the task, the more points awarded.
For each additional survey.
For adding feedback. And more points when each feedback is "Accepted" and given excellence stars.