how to use opening explorer

The opening explorer is showing results from the database for that position.  It is showing you have often in Chess.com's database each move was played along with the percentages of White winning, a draw, and Black winning.

This support article may make it easier to understand: https://support.chess.com/article/355-how-do-i-use-the-game-explorer

is the move at the top of the list the "best" ? or do you choose the one with "highest win percentage" ?

https://www.chess.com/explorer?moveList=c4+Nf6+d4&ply=2&origMoves=c4+h5

For instance, if f4/g5 has the highest win percentage for white, why is it not at the top of the list?

The move at the top of the list is the most popular.  Be careful when considering moves only based on win percentage - especially if it has not been played very much.

popular = best move?
what is the point of the game explorer including statistics on percentage of games won?
it seems contradictory for the most games won for a color to not be the most popular.

No need to be self-critical on this one.  It also took me a while to better understand how to read and properly utilize the opening explorer.

Keep in mind that the "best" move can be a bit arbitrary; many moves out of the opening can be equally good.

I recommend checking out this blog post which has some straight-to-the-point tips on reading the opening explorer: https://www.chess.com/blog/payetteforward/how-to-use-the-opening-explorer-on-chess-com-the-right-way

Here's a sample from the blog post I think you will find immediately useful:

• As long as a move has been played a few hundred times or more, it's an option.
• If there's a move that's been played 10,000 times and then others that have been played just a few hundred times, there's a clear choice about which move is the best.
• People focus way too much on the statistics of a move that scores better, and then they get overwhelmed because there are a lot of options, all of which have been played hundreds of times. What should they do? Forget about all that!
• As long as a move has been played a few hundred times and it's within a percentage of a decent score, then it's an option.

ok , thank you.

so just assume as long as you are in the bell-curve of GM games, it should be expected that its a good move
 the stats on win percentage are just there as extra info?

They can be useful.  For instance, if it's White to move and one of the options suddenly puts Black into winning 75% of the games, then there is likely something very bad about the move.

Alternatively, it can also help show the drawing potential of a particular line.  For instance, check out this line in a standard Petroff Defense: https://www.chess.com/explorer?moveList=e4+e5+Nf3+Nf6+Nxe5+d6+Nf3+Nxe4&ply=8

You'll notice that the win and draw percentages show the Petroff to lead to a lot of draws.  Particularly, the Qe2 line from here has a record of being extremely drawish.  So you could use this information to determine if you are willing to play for a draw or want to go down one of the more ambitious lines such as d4 or Nc3.

they should add an option to show the opening explorer as a bell curve 

the example helps a lot
thank you for the help💜