Simply put, the fork is a system upgrade, just like the iOS system of Apple's mobile phone needs to be constantly updated and upgraded. The fork can be divided into "soft fork" and "hard fork".
Soft forks are just upgrades to the network. The nodes before the upgrade are well compatible with the upgraded nodes and do not generate a new digital currency.
Hard forks are not the case. After a hard fork occurs, the nodes before the upgrade cannot be compatible with the upgraded nodes. The original blockchain will be divided into several independent chains, which may generate new digital currency.
The person who originally held the coin, after hard forks, theoretically has every coin after the fork.
Bitcoin updates a block every 10 minutes or so. The block records the transaction records and witness data that occurred within 10 minutes.
However, the maximum capacity of this block is only 1M. The size of this 1M block determines that the current transaction limit for Bitcoin is 5-7 per second. This is also the reason why the bitcoin network congestion problem is getting more and more serious and the cost is getting higher. For the long-term development of Bitcoin, bitcoin expansion is imminent.
Some people advocate directly expanding the block size of Bitcoin from 1M to 2MB, 3MB... even expanding according to demand, just like a road is too blocked, and roads are widened directly on both sides of the road.
Others advocate adding another layer of network to the Bitcoin network. Small transactions go directly to the newly added network and only need to be confirmed on the Bitcoin main network. This is like a road that is too blocked, not to widen the road, but to repair another small road directly next to it, so that small vehicles can take the path directly.