Many people who are new to bitcoin struggle with the term 'decentralised', and wonder what is meant by it.
Anyone can participate in the bitcoin network by running a node like bitcoin core.
You can download bitcoin core software from bitcoincore.org and run it on your laptop or computer.
There are over 17,000 bitcoin nodes scattered throughout the planet.
The node checks that each transaction is valid and actually happened. It also checks the hashing - that is how transactions are completed in a secure manner and there is no double-spending happening on the network.