I am having problem writing "Nandita" I comes out "ন‌নদিতা. N & D shall be juktakhar. What I am doing wrong?

If you are using Avro Phonetic:
It is working perfectly. Have you checked the "Auto-correct entries"? May be you have did something wrong there. If "nondita" entry is present there, delete it.

If you are using fixed keyboard layouts:
You have to type "hasanta" between two letters to make them Juktakkhar.
Like this: ন+ন+্‌+দ+ি+তা

This is the first Time I have used the Key Board. Thus, the auto-correct feature was not activated. I will try as you have suggested. I thought, according to your manual the juktakhar will originate automatically.

just type 'nondita'