To move bitcoins from one owner to another, you need to get confirmation from the network. Without this, the user has no right to dispose of the cryptocurrency, which is formally his property.
Immediately after the operation with the cryptocurrency, data about it is sent to the network to perform the corresponding transaction, after which this information is included in the block, thereby acquiring legitimacy for all participants in the system. This procedure is called online confirmation.
This whole process serves as a protective function and allows the system to prevent the reuse of the same coins. It is considered that with each inclusion in the block, the transaction receives one confirmation. After receiving six or more confirmations, the transaction is considered legal. Inclusion in the block is carried out during the generation of virtual coins.
In the classic version, an operation with bitcoins is considered complete if six or more transaction confirmations have been received from miners. This value was not chosen by chance - it is based on the theory that the probability of a fraudulent payment by a fraudster accumulating 10% of the hash is a very small percentage - something about 0.1%. In such a case, it is clear that obtaining six confirmations is a reliable guarantee to prevent criminal manipulation. That is, for attackers who do not have significant power, 6 confirmations are an insurmountable obstacle to an attack. In turn, people with more than 10% of the power will have no difficulty getting 6 confirmations in a row. However, possessing such computing power requires an investment of millions of dollars, which further reduces the risk of an attack.
At the same time, sites that accept bitcoins as payment for goods and services can set the required number of blocks to confirm the payment at their discretion.
It is impossible to determine exactly how long it will take to confirm the payment, since the length of the process directly depends on the work of the miners, that is, those people who are mining virtual coins. The person concerned must wait for confirmation until the next block is mined. The process of obtaining confirmation itself can take from twenty minutes to several days. The duration depends on many factors: network congestion, the number of pending operations in the queue, the risk of hacker attacks, and much more.
It is impossible to predict the exact amount of time it will take to include an operation in a block. But there is a way that will reduce the waiting time for a money transfer - it is enough to set high commissions.
To summarize, the process of including a transaction in a found block is called a transaction confirmation. Inclusion in 1 block is 1 confirmation, a transaction is considered confirmed when there are 6 or more confirmations. This function was introduced to protect against repeated spending of the same bitcoins (see "double-spending"), and therefore ensures the safety of operations with cryptocurrencies and user funds, respectively.