You’ll have to click on the icon on the top right corner, where you can log in.
If you don’t have an account yet, you’ll have to create one, if you already have one, proceed with “Log in“.
Here you have to fill all the required fields (*).
Now you have to activate your account through a token you get on your email adress.
After your account was activated and you logged in, you’ll have to choose a folder where your projects etc. are going to be stored.