There are many different ways to tune your ukulele, but the most widely used tuning is G, C, E, A. If you are used to the guitar - or any other stringed instrument for that matter - you may find the placement of the high G a little odd, but don’t worry you soon get used to it. This practice of having the high notes as the two outside strings of the instrument is known as re-entrant tuning.
For those with a baritone uke, the most common tuning would be D, G, B, E - a familiar sequence of notes for many guitar players, as it’s the first four strings of their six-string.
The simplest way to tune the uke is actually with a clip-on guitar tuner. All you need to do is attach this handy device to the headstock of the uke, pluck the string you want to tune, and the LED display will tell you if you are sharp or flat - it’s that easy and way more accurate than a set of pitch pipes.