Learn Turkish: Hediyeyi seçiyorum. - I am choosing the gift.

Hediye means "gift". We add the accusative suffix -i to show it is the specific, definite object of the verb (you are choosing the gift, not just any gift). Because hediye ends in a vowel, we must add the buffer letter -y- between them to prevent two vowels from touching, resulting in hediyeyi.

What if I was choosing a car (araba) instead of a gift? How would the accusative suffix change?

The accusative suffix changes based on 4-way vowel harmony. Since the last vowel in araba is a, the accusative suffix becomes -ı. With the buffer -y-, it becomes arabayı seçiyorum ("I am choosing the car").

Why is there an i in the middle of seçiyorum?

The verb root is seç- (choose). To add the present continuous suffix -yor (meaning "-ing"), we need a connecting vowel because seç ends in a consonant. Following vowel harmony, the e in seç means the connecting vowel must be i, giving us seç-i-yor-um.

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

In Turkish, you usually don't need to use the pronoun ben ("I") because the personal suffix at the end of the verb already tells us who is doing the action. The -um at the end of seçiyorum means "I am doing it".