Learn Turkish: Dün kararlaştırdığımız gibi, yarın sabah buluşuyoruz. - As we agreed yesterday, we are meeting tomorrow morning.

This uses the exact structure from your current lesson: verb + -dık + possessive + gibi. We take the verb kararlaştırmak (to agree) and add the participle suffix -dık. Because it's followed by a vowel in the "our" possessive ending (-ımız), the 'k' softens to 'ğ', giving us kararlaştırdığımız (that which we agreed upon). Finally, adding gibi (like/as) gives the meaning "as we agreed" or "in the way that we agreed".

The word kararlaştırdığımız is really long! How is the base verb kararlaştırmak formed?

It is built from the noun karar (decision). Adding the suffix -laş makes it a reciprocal action (doing something together), and -tır makes it causative (bringing something about). So, kararlaştırmak literally means "to bring about a mutual decision," which we naturally translate as "to agree" or "to set a plan."

Why does the sentence use the present continuous tense in buluşuyoruz (we are meeting) when talking about yarın sabah (tomorrow morning)?

Just like in English, Turkish frequently uses the present continuous tense (-ıyor) to talk about fixed, scheduled plans in the future. You could also use the standard future tense (buluşacağız), but buluşuyoruz sounds very natural and common for an arrangement that is already finalized.