Learn Turkish: Ders şimdi başlıyor. - The lesson is starting now.

Yes, the root is başla- (to start). This is an example of 'vowel narrowing', which happens when a verb root ends in a or e. When we add the -yor suffix, that final vowel narrows to ı, i, u, or ü. Here, the a in başla- changes to ı, becoming başlıyor (instead of başlayor).

Since başlıyor translates to 'is starting', where is the word for 'is'?

The 'is ...-ing' meaning is entirely wrapped up in the -yor suffix. Turkish doesn't use a separate helper verb like 'is' or 'are' for the present continuous tense. The verb root plus the -yor suffix does all the work!

Does şimdi always have to go in the middle of the sentence?

Not always, but it is very common! Time words like şimdi (now) usually go at the beginning of the sentence (Şimdi ders başlıyor) or right before the verb (Ders şimdi başlıyor). Turkish word order is flexible, but the verb almost always stays at the very end.

There is no word for 'the' before ders. How do we know it means 'the lesson'?