Thats all you do.
Just mount it.
Now it's a vertical monitor.
The games are written to display correctly on a rotated monitor.
For mame the switch is -ror or -rol, depending on if you need it left or right rotated.
(I.e. pacman, qbert, frogger, donkey kong, galaga, etc.)
(Most monitors can be mounted either way. I don't think they have made vertical only monitors in a long time.)
Later,
dabone