There are various types and sizes of ukulele. Standard tuning for each are shown below. Tunings are given from the top string (closest to the ceiling) to the lowest.
Scale length is the vibrating length of the strings, between the head-nut and saddle.
Re-entrant tuning means that the strings don’t run from low to high in pitch as you move through the strings. String four (closest to the ceiling) is tuned a fifth higher than the next string.