How do I find Current if I know only Voltage,Ohm's law?

You can't, given that information.

Ohm's law is about the relationship between voltage current and resistance. If you know any two, you can solve for the third. But you need to know two.

In your example, you need to know the current flowing in the load before you can complete the calculation.

You need to decide on how much current you want through that LED. 10 milliamps will light it nicely, 20 if you want it really bright.

You need to drop 1 Volt. For 10 milliamps, use 100 Ohms. For 20 milliamps, use half that.

You need to know the current draw of the LED for a proper number

(supply V - LED V)  / current draw
an average current draw is 15-20 Milliamps but can range from 10-50 so guessing is not the best option.

Use the manufacturers data sheet for the LED you are using.
It will tell you the "nominal" current to use.
This can often be found in the suppliers literature.
Then your resistor will need to drop the voltage DIFFERENCE across it at that current.
i.e. Resistor Volts + LED Volts (look it up 2V does not sound right) = Battery Volts
Ohms law will then give you the resistance of the resistor. R = V / I
Remember to check the power disipated by the resistor P = V x I to check
you are using a resistor capable of handling the power.

All good answers. You can use almost any kind of diode to get rid of 0.6 to 0.7 volts with a 100 ohm  or about 50 ohm varable resistor to dispose of about 0.4 volts. At max resistance, the LED will be dim. At minimum resistance, you may destroy the LED which will get about 2.4 volts if the 3 volt battery is a bit over 3 volts. A weak battery will be about right at zero ohms. If you have some rechargable NMH = nickel metal hydrid or nicad cells, these produce 1.2 to 1.3 volts, so you could replace one of the 1.5 volt cells with a lower voltage battery, or both, if you don't use the diode.
Volts = amps times resistance, so the variable resistor set to  ten ohms loses 0.1 volts if your LED needs 0.01 amps or 0.2 volts at 0.02 amps which are the two most common types of LED. In either case you can see ten ohms is not enough if the battery voltage is between 3.1 volts amd 2.3 volts, and 50 ohms is not enough, if you don't use a diode to get rid of about 0.6 volts.   Neil