When you visit the app at https://app.umbrellaanalytics.net/, you'll see the home page. If you're not logged in, you'll see buttons to the sign-in and sign-up pages.
Click "Sign in" and you will be taken to the following form:
Enter your email address and password, then click "Log in", and you'll be logged in and taken to the first dashboard.
Selecting the 'Remember me" option will mean you don't need to log in again on your next visit. We enable this feature by storing a cookie on your system. Clearing your cookies (or preventing them from being set) means that you'll need to log in again.