Yes, you can. However, you may find that you are more comfortable participating in the projects once you have learned in the Academy how uTest works and how to test with us.
If you are invited to participate in a project before you complete the Academy, we recommend carefully reading the project overview before you decide to accept or decline the invitation. There is no negative impact on your rating for declining a cycle. In fact, it can give your rating a small boost to decline a cycle, rather than accepting it but not participating or ignoring the invitation.