I have been very recently got familiar with OpenGL. I tried few tutorials to make simple cubes et all.

I want to make a drawing app on iOS. Lets say, for simplicity just freehand drawing in 3D plane. I have few questions:

1) What is the best approach? Lets say I can make viewport ready to draw opengl primitives. What after that?

2) How to convert 2D plane into 3D?

3) Will it be possible to rotate the whole view. What I mean is, if a user draws a cube with lines, how to rotate it with fingers?

Overall a simple drawing app. Let me know the best approach for this.