Can you explain what the T9 option on my cell phone messaging settings is supposed to do?

I have basic flip phone, not a smart phone. There is a T9 and a T9 Palabra option for texting. I know they try to predict what word I’m trying to spell. However, for example, I set the phone to T9 and tried to type the word “Test.” I typed “Te,” and it reverted to “Ted,” and it just went down hill from there. I back spaced to erase the “d” and it reverted to “Ve.” I was not able to type the word “Test.”

So, can someone enlighten me on this wondrous feature?