Ok, understood... so, what will happen if I my 10 addresses hold 1000BTC, divided in 100BTC each, and I want to do a tx of 250 to a new address?, will I have to send it from multiple sources? or Ledger will extract randomly money from each address until it matches 250?
I don't have a Ledger, but according to
this, it allows you to make use of coin control. That means, you can pick which of the unspent outputs to spend.
Say, for instance, that you have Unspent Transaction Outputs (or UTXO for short) #1, #2..., #9, #10, each loaded with 100 BTC. To spend 250 BTC, you'll have to pick three, your choice which (e.g., #1, #2, #3), and use them as inputs for a transaction. In that transaction, you'll spend 300 BTC, to create two outputs, one worth of 250 BTC (the recipient's) and another worth of 50 BTC (your change).