Time expressions in Spanish
por la mañana - in the morning
por la tarde - in the afternoon/evening
por la noche - at night
In some countries, people say en instead of por: en la mañana, en la tarde, etc.
Progress, Vol. 1
Progress, all volumes
Desirable difficulties
If studying feels effortless, you're probably not learning much. A bit of struggle during practice is a good sign. Difficulty isn't the enemy of learning; it's the mechanism.