Metronomes are an essential practice tool. While it takes a little effort to learn to play with one, the results will be worth it. A major key to successful playing is having rock-solid timing, and the best way to learn that is by using a metronome when you're practicing.
Modern metronomes are electronic. Look for models with a flashing light and which can be run with and without an audible sound. The lights may be LEDs (light emitting diode) or LCD (liguid crystal display). LCD displays are much easier to see outdoors than those with LEDs, but LEDs are better indoors or in darker environments.
Metronomes are generally set to click once for every beat in a measure. So, if you have a tune in 4/4 time, there would be four beats per measure. Each quarter note lasts for one beat; a half-note for two beats; and a whole note for four beats. It also means that there are two eighth notes per beat.
Most fiddle tunes are played between 200-240 beats per minute. That's at the upper limit of what most metronomes can handle, and it's also very hard to hear the metronome that fast. In this case, set the metronome to play at half speed - say 100-120 beats per minute - and then play two quarter notes per click.