Bitcoin transactions are verified by rules, not by a bank desk. A wallet creates a payment. The network checks whether that payment is valid. Then miners can place it in a block.
This process may sound technical, but the idea is simple. Every node can check the same facts. That is how Bitcoin keeps trust public.
Who checks the payment
Nodes check Bitcoin transactions first. They ask simple questions. Is the signature valid? Do the coins exist? Were those coins already spent? Does the transaction follow the rules?
If the answer is no, the node rejects the payment. If the answer is yes, the transaction can move forward.
What miners do
Miners collect valid Bitcoin transactions and build blocks. They do not get to invent coins or ignore the rules. Other nodes still check their work.
So, miners organize the payments. Nodes verify the rules. Together, they help the system work without a bank in the middle.
What to read next
Next, read proof of work explained. For background, see Bitcoin.org’s guide.