I am making a model I want to light up using led's
Can I connect them in a parallel or series circuit

You can do it either way, but in series the resistance builds as you add lights, so the lights get dimmer and dimmer as you add more of them. Parallel is the way to go. However, it can't be done by running one wire. It will require two wires between each light.

Be careful of three things. Make sure that the voltage is correct, the current supply isn't too great and remember that LED's have a positive and negative side. You may need a series resistor to cut down the current.
https://www.sparkfun.com/tutorials/219