Hi Vinod, 

Shared some details for your questions. 

1. Standard agent picks item from the queue right, how we push items in to queue?
   • This can be done by using Queue-For-Agent method from your activities. Using below parameters of the method, the items are queued to respective agent. 
     • AgentRuleset
     • AgentName 
     • MaxAttempts - Number of times for agent to process the queue entry in case of error or issue. 
2. How standard agent performs picks the item and process the item one work object?
   • Standard Agents generally query the queue and starts processing each one in the queue one by one. When the object is queued to Agent, the queue instance will have the pzInskey details of the workobject, which will be used by Agent to get the lock of the work object. Access to work object depends upon the access group associated to the Agent in Security tab. (Similar to the way any user tries accessing the work object of an application)
3. How it requeue when it fails how many times it will attempt?
   1. There are 2 scenarios for failure : 
      1. Agent couldn't get the lock of the work object
         • In this scenario depending upon the Auto Queue Management setting in agent rule, Agent will either discard the item or re-queue it for next run. 
      2. Error in processing the Object
         • Number of times it retries depends upon the settings we use while queuing it to the Agent using above method. By default is it is set to 1, but can be updated to the number required. 
         • If the Agent is unable to process the work object due to any error/issue even after multiple retries, it changes the queue status to Broken-Process . List of all the items updated to Broken-Process are available at Broken Queue which be found at Design Studio > System > Operations > Queue Management > Broken. This page will list all the objects that are failed along with the details of the Agent that tried processing it. 

Hope this gives you a good info to start with Agents.