Could you explain...?
Could you explain that for me, please?
Could you explain that in a little more detail, please?
Could you give us some more details on that?
Could you start again from the beginning?
Could you walk through it slowly?
Please give me all the specifics/details/fine points.
Tell me what you are doing.
Will you tell me what's going on here?
Tell me exactly what happened.
How could something like that just happen?
Don't leave out anything.
A: Could you explain that in a little more detail, please?
B: Sure. Let me walk you through it from the beginning.
A: Could you explain this in English for me, please?
B: Let me help you with that.