I've found a very clear answer to this question in this post:
Market Order vs. Limit Order vs. Stop Order: What’s the Difference
The order that is immediately executed is the Market Order.
When we want to buy or sell a more convenient price, instead, we use a Limit Order.
Limit Orders are sent to the "market", but are not executed by it until the price reaches the "limit" level.
Those orders are publicly visible because they are actually sent to the market and so the contribute to "move" the ask/bid columns.
Because they can’t be executed immediately, limits are held on the
order book, which is the electronic log of buy and sell orders for a
particular stock that cannot be executed at the current price.
Wikipedia defines the Order Book as
the list of orders (manual or electronic) that a trading venue (in particular stock exchanges) uses to record the interest of buyers and sellers in a particular financial instrument.
A matching engine uses the book to determine which orders can be fully or partially executed.
PLEASE, NOTE that here, "Stock Exchange" doesn't indicate the exchanges that we use to trade and to which we deposit our funds to use for trading, but, instead, indicates the "bourse".
Continuing with the explanation of a Limit Order
The order book also shows the market makers in the stock and their market size, or the number of shares they have available at that price.
The number of shares (and their prices) that are offered for sale by
market makers make up the ask side of the book, while the number of
shares (and prices at which) market makers will buy is the bid side.
The total amount of shares that are available for purchase and sale as
shown by the order books is the depth of market for that stock.
The Stop Orders, instead,
are also known as “stop loss” orders.
This alternative name comes from their role in the protection of an investor’s stock position – be it long or short.
A stop order has two parts: a trigger (or election) and an execution.
This is not a "real" order, but, instead, is an instruction that is given to the broker to create a Market Order (in case of use of a "simple" Stop Order) or a Limit Order (in case of use of a "Stop Limit Order") when the trigger is reached.
As Stop Orders are not actually sent to the market, they cannot be seen by it until the trigger is reached and a "real" Market Order or "Limit Order" is created.
The article is full of examples that helped me to better understand how the various types of orders work after a lot of searches and reading to try to understand the use cases for each type of order.
Now, finally, I have all (almost) clear: I only need to better metabolize them.
