Learn Russian: Это долгий день.

While Russian drops the word 'is' in the present tense, you must include a verb in the past tense. To say 'was', we use the past tense of быть (to be). Because день (day) is masculine, we use the masculine past tense form был. The sentence becomes Это был долгий день.

Why is there no verb like 'is' in this sentence?

In Russian, the present tense of the verb 'to be' (am, is, are) is almost always skipped. You just put the subject and the description next to each other. So, Это долгий день literally means 'This a long day', which we naturally understand as 'This is a long day'.

The word день ends in a soft sign (-ь). How do we know to use the masculine adjective долгий?

Russian nouns ending in a soft sign (-ь) can be either masculine or feminine, and you usually just have to memorize their gender when you learn the word. день is a masculine noun, so any adjectives describing it must take the masculine form, like долгий.

Why does the masculine adjective долгий end in -ий instead of the standard -ый?