How do I see/change Direct admin main password? For the root user?
There are 2 passwords.
root passwords for your VPS.
Directadmin admin password.
The Directadmin admin password is created by Directadmin during installation as you have seen.
But the Directadmin installation does never interfere with the vps or server root password, that's something completely different.
Root user = root = root password
There is no Directadmin password for the root user. There is a Directadmin password for the main admin account (sometimes called root admin, but that is different than the root user from the vps/server). It's just the admin password.
So it's important to use correct naming of things to prevent confusion.
So if you want your Directadmin admin password, you can do 2 things.
1.) Login via SSH as root user and look at the /usr/local/directadmin/scripts/setup.txt and in there you will see the directadmin admin password and the mysql admin password.
2.) If that password does not work (or not anymore) then you can change it by using this command as root in SSH.
passwd admin
then a new password is asked twice. After that you can use this password to login to Directadmin.