DC motors.

Hi,
Can I use a DC motor with an arduino uno. without a sheild or a transistor and how?

NO

what else do I need?

hilaaa: what else do I need?

A transistor, resistor and diode at least. See http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

if I don't have A transistor but I have Led and resistor?

hilaaa: if I don't have A transistor but I have Led and resistor?

Then you are stuffed as to driving a motor. Note a diode is not an LED.

Depends on the motor rating (volts and amps). I ran a tiny dc motor on the arduino bus just as an experiment. It “worked” but other things became flakey because of commutator noise .

What you need is a power stage rated for the motor volts and amps and controlled by the Arduino. At the motor terminals you need an RC snubber and a diode to keep some sort of control of the noise which the commutator and motor armature inductance generate.

But the chances are very slim that the poster’s motor is a <30mA stall current rated nanomotor… I’d
vote for a 2 orders of magnitude mismatch at least.

you never gave us the specs of your motor.

I have DC 3-6v Gear Motor

That's likely to have a stall current in the 0.5 to 1.5A range if its smallish but not ultra small. Some sort of motor shield or driver necessary.