"Launch" in the literal sense is to send something off, to start something on its way that will continue on its own -- to lauch a ship, to launch a rocket, etc. In its more general usage, it may be more often used when starting anything that likewise will continue by its own momentum. To launch a new business enterprise, e.g.
"Start" and "begin" can be synonymous and both can be transitive. But "start" is _more_ transitive, perhaps. I will start the car, or I will start a fire, but I won't say that I begin either of them. The fire begins (non-transitive) when I start it (transitive).
However, I can start to sing, and I can begin to sing -- no difference there. Likewise, I can start my song or I can begin my song, both transitive usages. Sorry, I can't really say why I begin a song but do not begin a fire; as a native speaker I just know. :-\
Commence is more formal. I would be very unlikely to use it in everyday speech. It is not usually transitive.
Start: Start the car. Start the show. Start doing something. Start (cause) a panic.
Begin: Begin the show. Begin doing something. Begin a new day.
Launch: Launch a new enterprise.
Commence: Commence with the show. Let's commence with the program.
[Edit] A non-native speaker who has studied these things might have more insight than a native speaker who "just knows".
Thank you very much. This is very helpful to me. Great.December 2015
Both the examples I gave for "commence" used the preposition "with", but that is not always needed. Other examples: "The meeting will commence in 5 minutes"; "Let us commence with a prayer."
As a native French speaker you have certainly found many English words that came from French. Many of them are very common and used by everyone in everyday speech. Often, however, when there is an Anglo-Saxon equivalent, the word of French origin is more formal or has a specific connotation.
An example: My wife's home "cooking" is very good, but we go to a nice restaurant for fine "cuisine".
A different example: In Anglo-Saxon times it was proper to use the word "shit" when necessary to discuss that in polite conversation. When the Norman French became the nobility with their high-class "excrement", the old English word became crude and vulgar.December 2015
I like khardy's explanations. They are always clear and at the same time detailed.
As a non-native speaker-philologist I could add some examples with 'with':
He begins the day wirth a walk.
I've started with a new language.
There are also some set expressions:
to start from scratch;
to begin with.
And I read in a sport article:
The team started off slowly.December 2015