the japanese word for speak is hanasu, and dekiru simply means able to do. it is the potential form of suru. I hope this helps and sorry about such a late reply!!

Nope, there's no such thing as Dasu instead of Desu. You can just leave it Da though. Its kind of informal. And boys do usually say Boku instead of Watashi.

Hey there thanks for the comments, lesson 14 has only just started in the works, please be patient and I'll get back to you