Here I would like to present some links that have helped me a lot.
1. ARVES
Not naming the Arves page first would be a silly idea. It's extremely useful every day, but the free editions of the magazine EG have been particularly helpful to me. I would say that studying the awards is essential for a tournament beginner. Not primarily because of the examples, but because of the judges' evaluation criteria. But there is so much more!
2. John and Sue Beasley website
The late John Beasley maintained a bunch of chess content on this website. The magazine British Endgame Study News deserves special mention.
3. Chess Problem Database Server ("Schwalbe, deutsche Vereinigung für Problemschach")
The Problem Database (PDB) can be quite useful.
4. GM Niclas Huschenbeth und Composition GM Martin Minski on Youtube
Wer des Deutschen mächtig ist, wird seine helle Freude an der Serie "Unglaubliche Studien" auf Huschenbeths Youtube Kanal haben. Diese umfasst 100 Folgen und ab Folge 49 ist Martin Minski mit dabei und erlaubt uns einen Blick ins Kompositionslabor. Ich habe eine Liste der Folgen erstellt, die ich bei Bedarf posten werde.
5. Chess Study Art
This expert page is maintained by Serhiy Didukh and offers a lot of information, including forums for some selected tourneys. For beginners like me there is a lot to learn by reading. But the tone there is often very rough, disrespectful or occasionally openly offensive.