Vtyjkyuk

I have a SOQL query in my server side controller Like

SELECT Id,PDCN__r.Id,PDCN__r.Name,PDCN__r.Brand_Trademark_Name__c,PDCN__r.Package_Standard_Name__c 
 FROM PDCNGrpJunc__c WHERE PDCN_Group__c = 'aBmq00000008UIUCA2'
 ORDER BY createdDate DESC

This Query Returns results when I specify PDCN_Group__c = 'aBmq00000008UIUCA2'. Now I have a method which takes a parameter groupId, when I write that groupId in SOQL Query I get Error-:
FROM PDCNGrpJunc__c WHERE PDCN_Group__c = '+groupId+'
^
ERROR at Row:2:Column:70
invalid ID field: +groupId+

public static list < PDCNGrpJunc__c > fetchJunction(String groupId) 
 System.debug('****groupId****'+groupId);
 List < PDCNGrpJunc__c > objJuncList = new List < PDCNGrpJunc__c > ();
 List < PDCNGrpJunc__c > objJunc = [SELECT Id,PDCN__r.Id,PDCN__r.Name,PDCN__r.Brand_Trademark_Name__c,PDCN__r.Package_Standard_Name__c 
 FROM PDCNGrpJunc__c WHERE PDCN_Group__c = '+groupId+'
 ORDER BY createdDate DESC ];

 // play for loop on objJunc and add each Junction to objJuncList List.
 for (PDCNGrpJunc__c c: objJunc) 
 objJuncList.add(c);
 
 // return the List of Junctions
 return objJuncList;
 

Could Someone Tell Me what I might be doing Wrong and How to pass the parameter into SOQL Query. Thanks!!

public static list < PDCNGrpJunc__c > fetchJunction(String groupId) 
 System.debug('****groupId****'+groupId);
 List < PDCNGrpJunc__c > objJuncList = new List < PDCNGrpJunc__c > ();
 List < PDCNGrpJunc__c > objJunc = [SELECT Id,PDCN__r.Id,PDCN__r.Name,PDCN__r.Brand_Trademark_Name__c,PDCN__r.Package_Standard_Name__c 
 FROM PDCNGrpJunc__c WHERE PDCN_Group__c = :groupId
 ORDER BY createdDate DESC ];

 // play for loop on objJunc and add each Junction to objJuncList List.
 for (PDCNGrpJunc__c c: objJunc) 
 objJuncList.add(c);
 
 // return the List of Junctions
 return objJuncList;
 

You have to use parameters as PDCN_Group__c = :groupId.

Accessing Variables in SOQL Queries

SOQL statements in Apex can reference Apex code variables and
expressions if they are preceded by a colon (:). The use of a local
variable within a SOQL statement is called a bind.

This example shows how to use the targetDepartment variable in the WHERE clause.

String targetDepartment = 'Wingo';
Contact techContacts = [SELECT FirstName,LastName 
 FROM Contact WHERE Department=:targetDepartment];