Learn Turkish: Getirdiğim kutuları salona yerleştirdim. - I placed the boxes that I brought into the living room.

This uses the object participle suffix -dik, a major B1 concept. In Turkish, to say "the boxes that I brought", you turn the verb getirmek (to bring) into an adjective modifying kutuları. You add -dik to the root getir-, and then add a possessive ending to show who brought them. So, getir + -dik + -im (my) becomes getirdiğim (literally "my-brought"). Notice that the k in -dik softens to ğ because it is followed by a vowel.

Why is there an -ı at the end of kutuları?

That is the specific direct object (accusative) case marker. You aren't placing just any boxes; you are placing the specific boxes that you brought. Whenever a direct object is pointed out specifically (especially when modified by a relative clause like getirdiğim), it must take the accusative ending: kutu (box) + -lar (plural) + -ı (accusative).

Why does salon (living room) take the -a ending here? Shouldn't it be "in" the living room?