The column everyone reads wrong
Quick answer: An opening explorer shows how often each move has been played from a position and how those games finished. The mistake is picking the move with the best win percentage. You should be filtering by a rating band close to your own, checking the game count so you're not reading noise, and using it to find where you leave theory rather than to choose moves you don't understand.
The explorer is the most useful free tool in chess and the most consistently misused.
Someone opens it, sees that a move scores 61 percent for White, plays it, reaches a position they've never seen with no idea what the plan is, and loses. Then concludes the tool is useless.
The number was true. It just wasn't about them. That 61 percent was produced by grandmasters who knew what to do on move fifteen, and inheriting their move without their understanding gets you nothing.
What the explorer is actually showing
Every explorer works the same way. You reach a position, and it lists the legal moves that have been played from it, with two pieces of information attached.
How many games reached that position and continued with that move. This is the frequency, and it tells you what's mainstream.
How those games finished, usually split into White wins, draws and Black wins as percentages.
The critical thing to understand is that this is a description of a database, not an evaluation of the position. It's history, not truth. An engine tells you how good a move is. An explorer tells you how often humans played it and how they got on.
Those two things diverge constantly. A move can score brilliantly because it sets a trap that works against unprepared opponents, while being objectively mediocre. Another can score poorly because it leads to positions that are hard to play, even though it's theoretically fine.
Most explorers let you switch between different databases, and that switch matters more than anything else on the screen. The master database contains games between titled players. The general database contains games from everyone at every level. Lichess's analysis board has both plus a rating filter, and it's free, which is why it's the one I'd point most people at.
Master games versus your rating pool
This is the single adjustment that turns the explorer from misleading into useful.
Filter to a rating band near your own. If you're 1400, look at games between 1200 and 1600 players. Not master games.
Why it matters: the moves that succeed at your level are not the moves that succeed at 2500. At club level, the openings that score well are the ones where the plan is clear and the opponent's mistakes are punishable. Sharp lines that require precision score badly at 1400 even when they're objectively strongest, because neither side plays them accurately.
I've watched this catch people out repeatedly, and you'll notice it immediately when you switch filters. A line that masters play constantly might barely appear in your rating band, and a move masters ignore might be scoring 58 percent among people your strength. That second move is often the more useful thing to know about, because it's what you'll actually face.
Use the master database for a different job: seeing what the mainstream continuation is and where theory currently sits. Use your own rating band to decide what to prepare against.
The two together answer different questions. "What is the best move here" is a master database question, and honestly an engine answers it better. "What am I likely to face on Tuesday evening" is a rating filtered question, and nothing else answers it at all.
The win percentage trap
A few specific ways the numbers mislead, worth internalising before you trust them.
Small sample sizes. A move played in 40 games showing 70 percent is noise. You need hundreds of games before a percentage means much, and explorers happily display three digit precision on a sample of twelve. Always read the game count first and the percentage second.
Survivorship in the master database. Master games get recorded when they're played in tournaments. Openings favoured by strong players against weaker ones will look inflated for reasons that have nothing to do with the moves.
Draw rates distort everything. At master level, a line scoring 40 percent wins for White might have a 50 percent draw rate, which means White almost never loses. That's an excellent practical result presented as a mediocre number. Look at the loss column, not just the win column, especially if you're playing Black and want safety.
Popularity is not quality. The most played move is the most played move. It's usually good, because lots of strong players chose it, but sometimes it's just fashion, and sometimes it's popular precisely because it's easy rather than best.
Colour bias in the display. Some explorers show the result bar from White's perspective regardless of whose move it is. If you're studying a Black repertoire, a bar that looks mostly white is a bar full of your losses. It sounds too obvious to mention, and I have still seen strong club players pick a line backwards because of it.
The habit worth building: before you accept any number, check the sample size, check the rating band, and look at all three result columns rather than one. That takes ten seconds and prevents most bad conclusions. If you want the underlying framework for what those numbers are describing, the Elo rating system explainer covers why results cluster the way they do at different levels.
Finding where you actually leave theory
Here's the use I'd rank above all others, and hardly anyone does it.
Take one of your own games. Play it forward in the explorer, move by move. Watch the game count.
At the start, thousands of games. Then hundreds. Then a sharp drop to a handful, then zero.
The move where the count collapses is the move where you left known territory. That's the single most valuable piece of information you can get about your own opening play, and it's usually much earlier than people expect. For a club player it's often move six or seven.
That tells you exactly where to study. Not the whole opening, not twenty moves deep, just the three or four moves around the point where you fall off. Fixing that one spot is worth more than reading a whole book, because it's the actual gap.
Do this with five recent losses and you'll find the same drop-off point appearing repeatedly. That's your weakness, identified with evidence rather than guesswork.
I ran this on a batch of my own games and the result was mildly humiliating. I had been telling myself I knew my main opening to about move twelve. The explorer said move seven, consistently, across four different games, and in three of those the move that took me out of theory was the same one. Twenty minutes of honest checking replaced a year of vague self assessment.
Then drill just that. Once the sequence is automatic you can push the drop-off point deeper, one small piece at a time. The opening trainer is built for exactly this kind of narrow repetition, and it's a far better use of an hour than browsing lines you'll never reach. The broader habit of reviewing your own games rather than studying abstractly is covered in how to analyze chess games effectively, and the explorer is the sharpest tool in that process.