The first bar (of varying color) at each bracket is the number of current unconfirmed transactions at that price bracket. The second bar (gray/blue) at each bracket is the number of confirmed transactions made today at that price bracket. The first bar changes color based on the site's estimation of how many blocks it will take for a transaction with that fee to be confirmed - green for the next block, yellow for a delay of 1-2 blocks, and so on.
Now, having said all that, that site is legendarily awful for suggesting a fee, and always grossly overestimates. The only time you need to pay its suggested fee is if you absolutely must have your transaction confirmed in the next block. If you can wait a couple of blocks, then you can usually pay a far lower fee and save yourself some money. The current suggested fee of 26 sats/byte would put you around 0.2 MB from the tip of the mempool, whereas if you look at a graphical representation of the mempool here (
https://jochen-hoenicke.de/queue/#1,8h), you can see that the mempool is pretty much emptying every couple of blocks. The minimum fee of 1 sat/byte would still get you confirmed within a few blocks.
