That response is too common. A dime a dozen.
Because, just like most atheists in forums - you're arguing about something you hardly get.
If you even have an inkling what the Triune God means, you wouldn't be asking that question.
Even your answer now, it shows either you didn't read the whole explanation in that link, or it went sailing over your head.
Your post is too revealing - it reveals you still don't get it. :shrug:
Anyway, that's the belief of Trinitarians.
If you have any problem with that belief - then,
for your sake, we better discuss it in the appropriate section.