Installation issue ; "Can't select database" message?

Hello all,
I’m a newbie on WP and I’ve been trying to set it up on my mac with the help of this video:
video

But after setting it up exactly as specified, I get to 6min40 and can’t seem to log in to the local host… I must have missed something but I have no idea what to try next.

I get the following message:

“We were able to connect to the database server (which means your username and password is okay) but not able to select the ‘wp39’ database.
Are you sure it exists?
Does the user ‘root’ have permission to use the ‘wp39’ database?
On some systems the name of your database is prefixed with your username, so it would be like username_‘wp39’. Could that be the problem?”

Any kind of help would be greatly appreciated!
Thanks a lot