Please pardon me for asking such a basic question.
Who checks that for a particular transaction, your wallet has sufficient money?
If Person A has to send Person B 5 BitCoins, which process validates that Person A wallet has the required amount for the transaction?
Thanks in advance!
That is actually a good question.
Miners verify transactions and put them in a block they try to mine. This means that every confirmed transaction is checked. So how do they check it?
The blockchain is a ledger that contains all transactions. There you can see when a coin was created and if a coin was spend and to which address it was spend. If there is no further address to which the coin was send, then it is still in the current address.
There is also a list of all addresses that hold unspent Bitcoins, so it is easy to check.
edit: also i think all wallets check if you have sufficient funds.