Here's why:
* "avoir cours d'anglais" means "have English class".
* "un quart moins dix" means "a quarter to ten" (or "9:45").
You can also say:
* "avoir cours d'anglais à neuf heures quarante-cinq" (have English class at 9:45)
* "avoir cours d'anglais à dix moins quinze" (have English class at fifteen to ten).
These are all correct ways to express the idea in French.