In order to use the Metabolizer you need to be logged in. If you do not have an account, you can either create a new user for you or log in as an anonymous user.
What difference is there between an anonymous user and a signed up user?
If you log in as anonymous user, you can access all the functionalities and tools of PathAct. However, all your work will be lost when you finish your session. If you create an account, you are given 10Gb of free disk space where you can save your data and results for future sessions.