The bitcoin, as well as other assets, submit to the market law of supply and demand. Buyers at the crypto exchange expose the requests for purchase, creating demand. Sellers offer requests for sale, creating a sentence.
For example, you want to buy bitcoin at the exchange. You can expose the request for purchase at a determined price and specify the volume (quantity of bitcoins which you want to buy). Your request will appear at the exchange in “glass” in a column of demand (bid). In this case, you need to wait when there is a seller who will want to sell you bitcoin at the price exposed by you. Also, you can acquire bitcoin instantly, having bought it on the current sentence (ask/offer) of sellers in “glass” at the crypto exchange.
The change in price in the market happens because of an imbalance of supply and demand on this or that asset. The price will fall if the number of sellers is more. In the fight for buyers, they will press the price down, reducing the offer price. Exactly, in the same way, the price will grow in case of excess of demand (buyers) in the market.