Difference between 学, 校 and 学校
"学校" is a compound word means "school"

The character "学" is also in other compound words like 小学 (primary school), 中学 (middle school), and 大学 (university)

The character "校" is also in other specific terms like 軍校 (military school), 警校 (police academy)


軍校 is short for 軍事学校
警校 is short for 警察学校
校 is just a short form of 学校 in these terms


Just like in English, the term "学校" (school) refers to the institution itself, it can be a whole building or buildings; a single room where a piano teacher teaches a few students can also be called a school (piano school)