I would like to make kid's cartoon characters (forx example: Bluey, Miracolous, Disney..), about 6-8 cm of height at max so I can put them on the decorative cakes for the photos.
For very basic model making, try tinkercad, it runs in your browser and gives you some basic controls to make objects.
Knowing what printer you have might allow others to give you advice, some printers behave differently than others in terms of hardware and system software.
What is your goal for 3D printing? Are you looking to print random knick knacks, functional prints, or just experiment?
Printers vary a lot in what they can do and their user-friendliness. You can go from simpler, almost plug and play models to more complex ones that require much more tinkering. They also vary a lot in price from a few hundred to thousands of dollars.