Question: Does en passant work only from the 5th row, or can it happen anywhere?
Answer:
A Pawn can only move 'en passant' ('e.p.') when on its own 5th rank. In essence, it pretends that an enemy Pawn moving for the first time has just advanced one rank instead of two.
The e.p. option is available for one move only. If not used on the first opportunity, it disappears.
The usual rules of legal moves apply. For example, a Pawn can't capture e.p. if it leaves its own King in check.
For details, see the link to the right under Suggested Reading.
More Chess Q&A