Learn Arabic (Modern Standard): درسنا التاريخ معا أمس.

The verb base is درس (darasa), which means "he studied". To change it to "we" in the past tense, we add the plural suffix ـنا (-na) to the end. Whenever you see a past tense verb ending in ـنا, it means "we" did the action.

Why does the word for "history" (التاريخ) have الـ (al-) attached to it if the translation doesn't say "the history"?

In Arabic, broad concepts, academic subjects, and abstract nouns usually take the definite article الـ (al-). So while in English we just say "we studied history", Arabic requires us to say "we studied the history".

How do you pronounce the beginning of التاريخ? Do we hear the "L" sound?

No, the "L" is silent here. The letter ت (taa) at the start of تاريخ is a "sun letter". When الـ (al-) comes before a sun letter, the "L" sound disappears and the sun letter is pronounced with a double, stronger sound. So it is pronounced "at-tareekh", not "al-tareekh".

Why does the word for "together" (معا) have a tall line (alif) at the end?

The word معا (ma'an) means "together". That tall line holds a double-dash symbol (called tanwin), which makes an "-an" sound at the end of the word. In Arabic, adding this "-an" ending is a very common way to create an adverb (a word that describes how an action is done).