The letter U is the 21st letter in the alphabet and is arguably the last vowel. It is based on the Semitic alphabet and the letter Waw, which was originally the letter Y. However, the V was then formed and then the U came from that.
The letter U has one look, whether it is the lower case or the upper case letter. This is very similar to the letter V but is curled at the bottom, instead of pointed. The U and V were commonly switched around during the Middle Ages but is something that has developed with the sound over time. By the 16th century, the U became the vowel. However, the upper case U was not recognized or accepte to be a letter for many years.
The U is commonly used with other vowels around, depending on the English language that you are using. The suffix OUS is common with the UK English but the U is commonly missed out when it comes to the US English. This is also common with other words such as favorite versus favourite and labor versus labour.
Like all of the other vowels in the alphabet, the U is only worth one point. This is something that is not worth playing on a bonus tile, unless you really have to.