If you only want to quick test your models you can start an interactive shell and execute your code there.
python manage.py shell
The above command starts a python interactive shell initialized with your Django project settings.
Then you can do something like:
from your_app_name.models import Dodavatel
p = Dodavatel(nazov='Petr', dostupnost=1)
p.save()
I do not recommend to use that code directly inside a view. Instead to create an item I would use a class based view like CreateView.