First, make sure your ukulele is in tune. If it's new, the strings will stretch each time you play and so it will need constant tuning for a few weeks.
If you are right handed, your right hand will strum, leaving the neck for your left hand. The strings are usually numbered 1 2 3 4 , 1 being the one at the bottom, 4 being the one at the top when you are holding the ukulele. They are Tuned as G (string 4 - the top) C (3) , E (2), A (1). Ideally you should have a tuner, and maybe even get the Ukulele tuned the first time at a shop.
If you have no tuner, there are plenty of smart phone applications and Online tuners (eg http://www.get-tuned.com/old_online_ukulele_tuner.php )
Now it makes the right noise, lets get to learning the parts.
To play the ukulele, you need to understand the fret board. You will notice it has many metal/wire looking bars up it, Between each bar is where you put your fingers, and these are called 'Frets'. So the first fret will be right up the "Nut", each fret that you move towards the sound hold is one number higher.
By putting your fingers on a string at the right fret, then plucking that string, it makes a a note. When you press the string down, the string sits on the fret wire. If you find your string is making a buzzing sound, or some chords are just not working out, then try work out if you are pressing it down fully, and make sure your finger is closer to the higher fret side.
Next-> Step 3 - Strumming