expression, i-adjective
not knowing what's what; unable to make heads or tails
Expresses total confusion about a situation; the speaker cannot grasp what is happening or what things mean. Often used when overwhelmed by information or chaos.
See also: 何が何だかわからない (なにがなんだかわからない)
説明が複雑すぎて、何が何やらわからない。
The explanation is too complicated; I can't make heads or tails of it.
初めて
On my first trip abroad, when I arrived at the airport I didn't know what was what.
Very similar in meaning; 何が何やらわからない uses やら for a slightly more emotive or colloquial feel, while 何が何だかわからない is a bit more straightforward.
A fixed expression combining 何 (what) with the particle が, the interrogative 何やら (something or other), and わからない (don't understand). The repetition of 何 emphasizes total confusion.