Learn Russian: Особенно трудно вставать зимой. - It is especially hard to get up in winter.

This sentence describes a general, recurring state rather than one specific, completed event. Because getting up in winter is a repeated, habitual action, the imperfective aspect (вставать) is required.

Where is the word for "it" in this sentence?

Russian doesn't use dummy subjects like "it" for general states or conditions. Instead, it uses impersonal constructions. The word трудно acts as an impersonal predicate, and the infinitive вставать attaches directly to it to mean "getting up is hard".

What case is зимой, and why doesn't it use a preposition like "в" to mean "in"?

Зимой is the instrumental case of зима (winter). To say that something happens during a specific season (like winter or summer) or time of day (like morning or evening), Russian simply puts the noun in the instrumental case without needing any prepositions.

How would I apply this lesson's topic to say "It is too hard to get up in winter"?

You would add слишком (too) right before the adverb: Слишком трудно вставать зимой. Because this is a simple impersonal phrase, the infinitive attaches directly without needing чтобы. If you wanted to practice using чтобы with a result clause of excess, you would phrase it slightly differently, such as: Зимой слишком холодно, чтобы вставать (It is too cold in winter to get up).