Play the first moves of an opening on the board, for either side, and the explorer names the position as you go: the opening family, the variation and its ECO code, using the same opening list as Lichess. At every step it also shows the moves that lead to other named variations, so you can see where your line branches off and what your opponents are likely to try.
Next to the name you see how many puzzles we have for that exact line. Every puzzle is a real mistake from a rated Lichess game between players rated 1800 or higher, checked with Stockfish. When you find the line you play, the Train button gives you only the puzzles from that line and the variations that follow from it, so you practise the traps you will actually meet.
Not sure where to start? Jump straight to a well-known line and play on from there: Italian Game · Sicilian Defense · Ruy Lopez · Caro-Kann Defense · Queen's Gambit Declined. The arrow keys step back and forward through your moves, and F flips the board.
If you would rather learn an opening from the ground up, start with one of the opening studies: they explain the ideas, the main variations and the most common mistakes at each rating level. The famous opening traps each have their own page with the losing move, the punishment and how to avoid it.