I’m currently learning Bangla and there are a few basic apps for iOS that present the letter along with it’s name, pronunciation, and how it is to be written (as in how to piece together the strokes to write the letter). It’s definitely geared towards kids, but the one I’m using is called BorKnow.

Also I’m using a book by Hanne Ruth Thompson called Beginner’s Bengali that does a good job at introducing the script.