What methods are used to determine access levels to classes or their members?

In C#, access modifiers are used to define the access level of classes and their members. The main ones are:

• public — access is open to everyone, the class or member is visible everywhere.
• private — access only within the class itself.
• protected — access within the class and its descendants.
• internal — access within the current assembly.
• protected internal — access within the current assembly and in descendants outside the assembly.
• private protected — access within the current assembly and in descendants within the assembly.

Example:

public class Example
{
    private int _privateField; // accessible only within Example
    protected int ProtectedField; // accessible in Example and descendants
    internal int InternalField; // accessible within the assembly
    public int PublicField; // accessible everywhere
}

These modifiers help encapsulate data and control who and how can use class members.