thank you for reaching out for help about this.
There are actually quite a lot of tutorials on classes and how they work. I'd suggest finding a blog, book, or video and just work through it.
However for your particular issue I'd suggest setting up your minion as it's own class. Then setting up your boss with a spawn method that creates minions.
You'll need the super constructor for this to work.
The idea behind this is that your class "hierarchy" will look like this:
         Object
           | 
        Character
        |
      Boss
What this shows us is that all of your classes will be children of Object. Boss is a child of Character. It is common to hear this relationship described as a "is a". i.e. Boss is a Character.
Moving forward.
Let's imagine your character class looks like this:
class Character(Object):
    def __init__(self, name="Placeholder",
                 level=1, hp=10, attack=10, 
                 defense=10, experience=0):
        self.name = name
        self.level = level
        self.hp = hp
        self.attack = attack
        self.defense = defense
        self.experience = experience
Spawning a minion from you boss is rather simple. Try constructing a new character with the relevant stats. This might look something like the following:
class Boss(Character):
    '''
     Defines the boss class.
     Which by default has the following values:
       Name: "Boss"
       level: 100
       hp: 10000
       attack: 1000
       defense: 1000
       experience: 10000 
    '''
    def __init__(self, name="Boss", level=100,
                 hp=10000, attack=1000, defense=1000,
                 defense=1000, experience=10000):
        super(Boss, self).__init__(
            name=name, level=level,
            hp=hp, attack=attack,
            defense=defense, experience=experience
        )
    def spawn(self):
        '''
        Spawns a single minion
        '''
        return Character(name="Minion", level=self.level,
                         hp=round(self.hp / 4),
                         attack=round(self.attack / 4),
                         defense=0, experience=0)
There are tons of other ways to accomplish this using other paradigms, but this is a good starting point for OOP. If you'd like a little help with types and even spawning different kinds of minions I'd suggest researching enums in python.
EDIT: Example including Minion subclass
This would change your inheritance tree like so:
         Object
           | 
        Character
        |      |
      Boss    Minion
Which, again. Means both your Boss and Minion are children of Character and thus by extension are children of Object.
You can describe this as: "Boss and Minion are Characters".
Edited code below:
class Character(Object):
    def __init__(self, name="Placeholder",
                 level=1, hp=10, attack=10, 
                 defense=10, experience=0):
        self.name = name
        self.level = level
        self.hp = hp
        self.attack = attack
        self.defense = defense
        self.experience = experience
class Minion(Character):
    '''
    TODO: define any special attributes,
          abilities, etc of the minion
    '''
    pass
class Boss(Character):
    '''
     Defines the boss class.
     Which by default has the following values:
       Name: "Boss"
       level: 100
       hp: 10000
       attack: 1000
       defense: 1000
       experience: 10000 
    '''
    def __init__(self, name="Boss", level=100,
                 hp=10000, attack=1000, defense=1000,
                 defense=1000, experience=10000):
        super(Boss, self).__init__(
            name=name, level=level,
            hp=hp, attack=attack,
            defense=defense, experience=experience
        )
    def spawn(self):
        '''
        Spawns a single minion
        '''
        return Minion(name="Minion", level=self.level,
                         hp=round(self.hp / 4),
                         attack=round(self.attack / 4),
                         defense=0, experience=0)
     
    
return Character(name="minion", at=0,....)that's all and it goes underspawn. This creates a new character with the specified stats. I don't know if you need aBoss.__init__and I know the Boss init shouldn't take Minion as a default name.Minionis its own class. Can you share a stub of the Character class as well? Perhaps the Minion class too so folks know what the initialization will look like.super().__init__(...)