[solved] USB to Serial TTL Question

So if I use the unit that has +3.3 and +5 Vcc out and use the +5 Vcc out and the Rx/Tx that measure under +5volts I should be ok?

What the heck is the purpose of having +3.3 Vcc if Rx/Tx does not change to 3.3 and remains under 5?

I am trying to figure out why this USB to Serial was made this way and how it could be used practically!!!