Learn Turkish: Nereye gidiyorsun? - Where are you going?

In English, 'where' is used for both location and direction. Turkish is more specific. Nerede means 'where at' (location), but here the verb is about movement. To ask 'where to', you must use nereye.

How do the suffixes in nereye work?

The base word is nere (what place). To say 'to what place', we add the directional suffix -e. Because nere ends in a vowel, we must add the buffer letter -y- between them, giving us nere-y-e.

The dictionary form of 'to go' is gitmek. Why does it say gidiyorsun with a 'd'?

This is due to a spelling rule called consonant mutation. When a verb root ends in a hard t (like git-) and gets a suffix starting with a vowel (like the present continuous -iyor), the t softens to a d to make it smoother to pronounce.

Where is the word for 'you' in this sentence?

It is attached to the very end of the verb! The suffix -sun in gidiyorsun means 'you' (singular). You can include the separate pronoun sen at the beginning for emphasis (Sen nereye gidiyorsun?), but it is entirely optional.