The first thing to do before playing an instrument is tuning it. It is essential to be in tune if you want to play a rendition of a song on a ukulele and need people to recognize what you are playing. On top of that, it allows the instrument to sound good with an effect that can be reproduced every time you play.
There is nothing more distracting and annoying than having to wonder how your instrument was tuned when you were composing a song. With that in mind, the tuning of an instrument depends on what people usually want to play. There is not a right way to set how the strings should sound or what note each string should make as long as people know what they are doing.
It is more convenient to have a standard tuning when other people are playing along or when starting to play an instrument for the first time. There are different standard tuning for the ukulele. The most used one is what people call the re-entrant tuning in G or high-G tuning.
The easiest way to tune an instrument is to get an electronic tuner. These devices are very accurate and make the whole tuning process really fast. If you do not have a tuner, I would recommend to buy one because it is a good investment and will be useful any time you will need to check the correct tuning of the ukulele.
High-G Tuning has GCEA as the notes of each strings starting from the top one. The first string is higher than the second one and that is why it is called the re-entrant tuning or high-G. Pluck the first string and check the tuner. If it is not a G, turn the knob corresponding to the string until the tuner shows G. Repeat that with each strings.
Another standard tuning is the Low-G one. Instead of having the first string higher than the C, it is lower in sound. This is a tuning that most guitar players like to use because of the resemblance with the 4 last guitar strings.
In general, it takes a few days up to a week until the strings are set. So during that time you will have to check the tuning frequently. Indeed, the strings need time to stretch and acquire their equilibrium compared to when no tension was applied on them. By doing so, your ukulele should stay in tune most of the time.