Can anyone explain me how a splitter has to be hacked?
The Tutorial was too fast and I haven't understand what I have to do.

I assume you mean shards, like the one you get from Meredith Stout.

Stout's shard you access via the main inventory screen (default key: "I").
Hover the cursor over "Journal" and then click on "Shards". Scroll down the list to Stout's Militech Datashard, click on it, and above the description to the right, the prompt to "Crack Security" will appear (or not(?), depending if you've unlocked enough of your netrunner capabilites by having enough Intelligence or the corresponding netrunner perk(s)).
Press the key shown (default key: "F"), and it will switch over to the breach interface.
And from there it's like any other breach - match the shown sequence by combining the right hex values on the matrix, and bingo (in case of Stout's Militech Datashard the "Neutralize Malware" option is obviously the one you're primarily after, managing to get the other one ("Datamine/Copy Malware") too is optional).

Other instances of decrypting/hacking shards should go the same way.

You can read up on the tutorial popups at any point later, by the way.
In the Database (press "I" for the inventory, and then click on "Database" in the lower right corner) that collects all the lore on the world, weapons, vehicles, characters, places, etc. There's a separate tab for the tutorials (question mark icon).

Thanks for the answer.
After several trials I begin to understand how it works.