Questions about the price
Where does the price come from
From Kraken. The page reads the last traded price on the XBT/USD market through the exchange public interface, and prints the time it was read next to it.
What is XBT
Kraken names bitcoin XBT rather than BTC, following the currency code convention where X marks something no country issues. XBT/USD and BTC/USD are the same market.
How often does the price update
Every five minutes. The chart and the thirty-day table use one closing price per day, so they change once a day rather than continuously.
Why does another site show a different price
Every exchange runs its own order book and they drift apart by a fraction of a percent. Aggregators publish an average across several venues, which is a third number again. The Coinbase quote on the converter page shows the gap on the day.
What is a satoshi
The smallest unit of bitcoin, one hundred millionth of a coin. One bitcoin is 100,000,000 sats, and small payments are usually quoted that way.
Is this the price I would pay
No. A market price is where the last trade happened between two other people. An exchange adds its spread and its fee, and a card purchase adds more again, so the amount that leaves your account is higher than the number here.
Can I buy bitcoin on this site
No. This is a price page. It holds no money, takes no account and executes no order.
Is any of this advice
No. The page reports what an exchange quoted and nothing more. It is not financial advice, and what bitcoin does next is not something this or any other page knows.