Italo Trains

Yes, possibly, and also letting passengers off.

Something trains are able to do very easily. Stop at an intermediate station for only 2 minutes, long enough for people to get on and off and then its on is way again. There is only one stop between Termini and Florence, Rome's other big station, Tiburtina.
Venice to Rome Termini will stop at Venice Mestre, Padua, Ferrara, Bologna, Florence, and Tiburtina.

I don't know the answer, but wanted to countermand the other responses which strike me as a bit sarcastic. Where I live (near NY City) some trains will not pick up passengers at certain stops at certain times of day. You can only get off the train. And, at other times of the day, the opposite is true -- you can only board the train. So I think your question is very legitimate.

I only wanted to make sure that **I did not have to get off** to make any kind of
connection.

If you have to get off it will show that it will be listed as a different train, with the arrival time for the first train and a departure time for the second train.
The trips you list (Roma Termini to Firenza SMN and Venezia SML to Roma Termini) are all main routes, no changing needed.

I have seen many posts where posters describe places where you change trains as "stops" or thinking stops are where you change trains. Possibly unfamiliarity with terminology.
Also posters asking for "direct" trains for impossibly complicated connections because they say changing trains would be too complicated (small town A to small town B in a different country), where you have to change 2 or 3 times, again unfamiliarity.

One point to note..... according to the Italo website, the official designation for the station in Venice is Venezia S. Lucia and not "Venezia SML".

trust,

There may be several stops, but you'll have the same reserved seat for the duration of the trip. If that wasn't the case, another train and number of changes would be listed.

I don't know the answer, but wanted to countermand the other responses
which strike me as a bit sarcastic

The responses weren't sarcastic at all, IMHO. Without knowing exactly why trustinsoul asked the question, that the trains are picking up or dropping off passengers at stops is a straightforward response.

Some new travelers to Italy are a little nervous about random individuals accessing the trains at stops, specifically when their luggage may be stored on the ends of the carriage. Until offered an explanation for the question, it wasn't clear why it was asked.

You've nothing to worry about, trustinsoul. As has been explained, you'll just keep your seat until you arrive at your final destination. :O)

Thanks for the advice - I actually booked the Rome-Florence, and the Florence-Milan this morning
with Italo and was happy with the prices and found their website easy to use. Note: I did have to authorize American Express to allow the charges. As always, I appreciate all the help! Ciao!