If a word has a "Q", the next letter must always be a silent u. That is, you write a "U" but don't pronounce it. And after that "U", always comes a vowel.

Similarly, if after a "G" comes a "E" or "I", it is pronounced differently depending on if there is a silent "U" after the "G".

However, sometimes we want a non silent U after a Q or a G. In that case, we write "ü".

So u and ü are literally the same letter in spanish. We call the 2 dots "diéresis", maybe it's similar in German.

[–] luciferofastora@feddit.org 1 points 20 hours ago

However, sometimes we want a non silent U after a Q or a G. In that case, we write "ü".

Then it's similar concept: the letter combination qu is pronounced differently than q-u separately, and the diéresis indicates that they should be pronounced separately.

In German, Diärese refers to the separate pronunciation of vowels, so the concept rather than the indicator. The indicator is called Trema, but it's rarely used in German itself anymore. You just have to learn how things are pronounced, because of course we have to make things difficult. Can't have learning German be easy, can we?