I am a new player and I'm doing some research on meta decks. Some of the articles on the Magic website have a stats section when talking about certain decks and I can't figure how how to read them. I've attached a screenshot of what I am talking about. The middle and right charts are self-explanatory, but I am more interested in knowing how to read the left chart.
Those are mana costs to cast cards in your deck. The numbers represent the total amount of mana to cast. For instance, if you have a card that costs 2 green and 1 blue, it will fall under the 3-cost pile.
My guess for the 23 0-cost cards is that they are primarily lands, as 1/3 is roughly the recommended amount of lands for a deck. In general, you want as many cards to be on the left end of that spectrum as possible, as it's not always guaranteed that you'll have enough lands to cast the more expensive cards.