Learn Turkish: Şimdi yağmur yağmıyor.

The verb root is yağ (to precipitate/rain). To make it negative, we add a negative suffix. Because the vowel in yağ is 'a', 4-way vowel harmony tells us to use -mı. Then we add the present continuous suffix -yor. Together, yağ + -mı + -yor makes yağmıyor (it is not raining).

Why do we need both yağmur and yağmıyor? Doesn't that mean 'rain is not raining'?

Yes, literally it translates to 'the rain is not raining'! In English, we just say 'it is raining,' using 'it' as a dummy subject. In Turkish, you must specify what is falling. You use the noun yağmur (rain) as the subject, paired with the verb yağmak (to fall/precipitate). You will see the exact same pattern with snow: kar yağıyor (it is snowing).

Is there a word for 'it' in this sentence?

No, there isn't a separate word for 'it'. In Turkish, third-person subjects ('he/she/it') don't require personal endings on the verb. The present continuous suffix -yor with nothing attached after it automatically implies 'he,' 'she,' or 'it' is doing the action.

How do I pronounce the ğ in yağmur and yağmıyor?