How to use MinMaxSlider with serialized property?

Hi everyone! I tried so much to solve this, and I don’t know what else to do!
I need to show a minmaxslider on my custom editor, but I can’t get my head around the BeginProperty stuff. It simply do not make any sense to me. Here is my code, can anyone help me?

using UnityEngine;
using UnityEditor;

[CustomEditor (typeof(FliesSystem))]
public class FliesSystemEditor : Editor {

	private SerializedObject instance; 

	private SerializedProperty velocity;
	private SerializedProperty minVelocity;
	private SerializedProperty maxVelocity;
	public void OnEnable()
		if(instance == null) instance = new SerializedObject(target);

		velocity		= instance.FindProperty("velocity");
		minVelocity 		= instance.FindProperty("minVelocity");
		maxVelocity 		= instance.FindProperty("maxVelocity");

	public override void OnInspectorGUI()


		GUILayout.Label ("Animation Settings", EditorStyles.boldLabel);

                //PSEUDO CODE:
                //get SERIALIZED min and max velocity from MinMaxSlider (I don't know how)
                //velocity.floatValue = Random.range(min,max);

                //PLEASE HELP!!


Thanks in advance!

You asked something similar here, so I’m cross-answering.