Does anyone know how Vocaloid works?

[Petzbreeder]

I can't work out how to make Vocaloid say anything other than "Ooh Ooh Ooh".

Regardless of what I type, that is literally the only sound I can make it say most of the time.
I'm using the Kaito and Megpoid voces (Mostly Megpoid).

I just can't figure out how the program works. I've tried typing individual syllables, and I've tried typing whole words. It just never says what I want it to say.

If I wanted to for example, type the lyrics to the Backstreet Boys song "I want it that way" into Vocaloid, how do I type it to make it say the actual words?

Here is a link to the song.

Here are the lyrics to the beginning of the song:
You are my fire
The one desire
Believe when I say
I want it that way

I would love to be able to recreate pop songs using a combination of Fruityloops and Vocaloid.

Edit: I worked it out after watching many tutorials.