Move object along the path,Move an object along the fixed path

Use Navigation mesh agent.

This component is attached to a mobile character in the game to allow it to navigate the scene using the NavMesh.

 public bool SetDestination(Vector3 target);

Sets or updates the destination thus triggering the calculation for a new path. Note that the path may not become available until after a few frames later. While the path is being computed, pathPending will be true. If a valid path becomes available then the agent will resume movement.

 using UnityEngine;
 using System.Collections;
 
 public class NavmeshMovement: MonoBehaviour {
 
     public GameObject targets;
     public NavMeshAgent mNavMeshAgent;
     public    int i ;
     float dist;
 
     void Start () {
         
         mNavMeshAgent = GetComponent<NavMeshAgent>();
         mNavMeshAgent.destination = targets.transform.GetChild(i).transform.position; 
     }
     
     // Update is called once per frame
     void Update () {
 
     if(mNavMeshAgent.enabled)
     {
 
             dist = Vector3.Distance(targets.transform.GetChild(i).transform.position,transform.position);
             mNavMeshAgent.destination = targets.transform.GetChild(i).transform.position;
         
                     
         if (dist < 2)
         {                
             i++; //change next target      
 
 
                 if (i < targets.transform.childCount )
                 { 
                     mNavMeshAgent.destination = targets.transform.GetChild(i).transform.position; //go to next target by setting it as the new destination
                 }
                 
                 //check if at end of cycle, then reset to beginning of cycle
                 if (i == targets.transform.childCount )
                 {
                     Debug.Log("NAVIGATION FINISHED. RESET.");
                     i = 0;
                     mNavMeshAgent.destination = targets.transform.GetChild(i).transform.position;
                 }
         }
     }
  }
             
 }

targets are the fixed path points for movement of your navmesh agent.

NavMeshObstacle

An obstacle for NavMeshAgents to avoid.

A NavMeshObstacle is cylindrical in shape and can move around the surface of the NavMesh with a specified velocity. By default, the obstacle will only affect the agent's avoidance behaviour rather than the pathfinding. This means that the agent will ignore the obstacle when plotting a path but will sidestep around it while moving along the path. If carving is enabled, the obstacle will create a temporary "hole" in the NavMesh. The hole will be recognised by the pathfinding, so paths will be plotted to avoid the obstacle. This means that if, say, an obstacle blocks a narrow gap, the pathfinding will seek an alternative route to the target. Without carving, the agent will head for the gap but won't be able to pass until the obstacle is clear.

Attach Navmesh Obstacle Component on your obstacles then your agent will avoid collision with the obstacles. For More Navmesh Obstacle description see this Link