what's what; heads or tails
Used to express confusion when one cannot make sense of a situation. Often followed by わからない or similar phrases.
The explanation was too complicated; I couldn't make heads or tails of it.
It happened so suddenly that I have no idea what's going on.
A set phrase combining the interrogative 何 (what) with the copula だ, literally 'what is what', used idiomatically to express bewilderment.