Parameters allow Variables to be passed into a method by the caller. For example:
using UnityEngine;
public class Example : MonoBehaviour
{
    private int _Counter;
    // _Counter starts at 0.
    private void Awake()
    {
        // Call the AddValue method using 2 as the "value" parameter.
        AddValue(2);
        // _Counter is now 2.
    }
    private void AddValue(int value)
    {
        // Add the given "value" to the "_Counter".
        _Counter += value;
    }
}