We spell proper nouns with a capital letter:
Sarah Wael
London
Spain
Havard University
European Eunion
We use capital letters for festivals:
Ramadan
Deepvali
Easter
Christmas
Thanksgiving
We use capital letters for people's titles:
I was talking to Doctor Wilson recently.
When we give the names of books, films, plays and paintings, we use capital letters for the nouns, adjectives and verbs in the name:
I have been reading The Old Man and the Sea.
Beatrix Potter wrote The Tale of Peter Rabbit.
You can see the Mona Lisa in the Louvre.
Sometimes we use a person's name to refer to something they have created:
Recently a Van Gogh was sold for 15 million dollars.
We were listening to Mozart.
I'm reading an Agatha Christie.