[SalesForce] Fire Trigger Only When Stages Moves to Closed Won

Although you don't have much in the way of experience with code, it seems clear that you do know what generally needs to be done.

A few extra things to keep in mind to help make it even more clear what needs to be done:

• Instead of being on a Case, it appears that you'll want this trigger to be on CDR__c
• From item #2 in your question, your approval process has a final approval or rejection action that updates your record. This means that an update trigger is more appropriate here
• From the documentation on Apex Triggers an after trigger is more appropriate here

  • After triggers are used to access field values that are set by the system (such as a record's Id or LastModifiedDate field), and to affect changes in other records, such as logging into an audit table or firing asynchronous events with a queue. The records that fire the after trigger are read-only.

• Following trigger best practices, you'll want to assume that you'll be processing more than one record at a time. Doing your comparison inside a for loop over the trigger.new context variable is a good idea
• Callouts inside of a loop are dangerous

Those last two points present an issue here. The JIRA REST API looks like it can only create one record at a time. The JIRA docs provide another method for automating creation of JIRA issues, and I would strongly recommend using that instead.

The basic form of your trigger will be

Trigger CDR_Create_JIRA_Issue on <<object name>>((before|after)(insert|update|delete|undelete){
    // Declare a collection (that is, a set, map, or list) to hold the Ids of the
    //   objects that will become JIRA issues
    // Set<Id> -> the data type
    // = new Set<Id>(); -> One way to initialize a new set
    // Variables need to declared prior to being used, and most (if not all)
    //   need to be initialized prior to use as well.
    Set<Id> jiraIssueObjectIdsSet = new Set<Id>();

    // The other JIRA class we can use expects a List of SObjects instead of simply Ids
    List<CDR__c> jiraIssueCDRList = new List<CDR__c>();

    // Also probably a good idea to just define the things that won't change from
    //   JIRA issue to JIRA issue
    String objectType = 'CDR__c';
    String projectKey = 'SFDC'; // Change as appropriate
    String issueType = '1'; // Change as appropriate

    // Iterate over the trigger context variable 'trigger.new', and figure out which
    //   records need JIRA issues created for them
    // CDR__c myCDR -> defining the 'loop variable' that we can use inside the loop
    // :trigger.new -> tells us what to iterate over, each single item from trigger.new
    //   is placed into the loop variable, and the loop variable is updated
    //   after we reach the bottom of the loop
    for(CDR__c myCDR :trigger.new){
        // We use dot notation to access data inside of records
        // Replace 'yourField__c' with the actual name of your field
        // For boolean (i.e. true/false, or checked/unchecked in the case of a checkbox field)
        //   fields, we don't need to explicitly say field == true because
        //   true == true evaluates to simply true
        if(myCDR.yourField__c){
            // This is a record for which we want to create a JIRA issue
            //   add the id to our set
            jiraIssueObjectIdsSet.add(myCDR.Id);

            // If you want to use the better method of creating JIRA issues,
            //   then you'll want to add this CDR to the list of CDRs we want to create
            //   issues for
            jiraIssueCDRList.add(myCDR);
        }
    }

    // While we could have just created the JIRA issues in the previous loop, it's
    //   generally a good idea to separate gathering Ids from doing work on those Ids

    /*for(Id jiraObjectId :jiraIssueObjectIdsSet){
        // Method call to create a JIRA issue here
    }*/

    // The above will work (up to a point), but there is a more appropriate way
    //   to do this.
    // If you want to use the loop + REST API for JIRA, uncomment the loop above
    //   (remove the "/*" and "*/")
    // 
    /*
    JCFS.API.createJiraIssue(projectKey, issueType, jiraIssueCDRList, Trigger.old);
    */
}

Hope you can take things from here.