Can only boot up guest session on Raspberry pi 3 - Please Help

I’ve been trying to boot up Ubuntu Mate on RPI3 for the first time and I can only boot up the guest session.

How do I do a full boot because I don’t see it anywhere…

If I recall, when uMate first booted on my RPi, there was a screen for putting in a user’s name and password. Once that is past, you don’t see it again but the System>Administration>Users and Groups selection gives you the option of adding users/passwords, or you can do it from the command line: “sudo adduser yourusername”.

I have the same issue.
I tried, but then it asks for root password, or the password for the guest session.
I don’t have either of them.
What should I do?