Capitalise (British spelling) or capitalize (North American spelling) means to make one or more letters upper case. The first letter of a sentence is capitalised in many languages, as are the first letters of proper nouns such as names of people and places. In German, however, all nouns are capitalized. It is the only language to do that.
In the Latin alphabet, which is used in English, these are the upper case or capital letters:
These are the lower case letters: