Usually wallets will construct the transaction and either sign it or delegate signing to a signing device (i.e. hardware wallet). Once the transaction is signed, the wallet will tell a node (or a server connected to a node) to broadcast it. When a node receives the transaction, it tells (gossips) about the transaction to all the other nodes it is connected to. Due to the viral nature of gossip protocols, it does not take much time to propagate the transaction across the whole network. Miners find out about the new transaction in seconds.
Discussion
So, these transaction are to be signed before they are broadcasted?
Yes. It's the only way to create a valid transaction
Valid also means confirmed,correct?
No. Valid means that the transaction adheres to the rules; that the inputs and output amounts match, that the signature is valid, etc...
Confirmed typivally means a transaction has been put into a mined block.
Can confirmed trandactions that had been put into mined blocks be unvalidated or never been validated?
Not successfully. The network would reject the block and the miner would have wasted time and money creating it.
So all the confirmed transactions that were put into the mined block had already been signed and broadcasted?
Yes.
Construction.
Signing.
Broadcasting.
Mempool.
Confirmed.
You should look at mempool.space. See what doesnt makes sense to you, and come back with questions.
On the left is the mempool, these are unconfirmed transactions, ordered in chunks of "candidate blocks" by their chances of making it into the next mined block. On the right are the mined blocks.
Clicking a candidate block in the mempool shows you the transactions waiting to be confirmed.
Clicking a block shows you the transactions that were confirmed. You can click transactions to get details about them, including their amount, the fees paid, etc...
And this signing can be done thru mobile phones?
Can signing be done using mobile/android phones?