Populate Description field with the user first name who creates or updates the record by using userInfo standard keyword , and also does not allow user to delete the record. Write it's Test class also.

Example : If user is Test User "Author Last updated by user firstName (use userInfo to fetch firstname)"

....TRIGGER....

trigger PopulateDescription on Account (before insert, before update, before delete){
    If(trigger.isInsert)
    {
        for(Account Acc: Trigger.new){
            Acc.Description = 'Account Created by '+ userInfo.getFirstName(); 
        }
        
    } else
        If(trigger.isUpdate)
    {
        for(Account Acc: Trigger.new){
            Acc.Description = 'Account Last updated by '+ userInfo.getFirstName();   
        }
    }
    
    if(Trigger.isDelete&&Trigger.isbefore){ 
        for(Account Rec:trigger.old) 
        {
            
            Rec.adderror('You Cannot Delete the Account Record');
        }
    }
}
....Test Class....
public class PopulateDescriptionTest {
    @isTest
    public static void populatedescription(){
        
        Account acc = new Account();
        acc.Name = 'Test';
        acc.Description = 'Account Created by '+ userInfo.getFirstName();
        insert acc;
        
        acc.Description = 'Account Updated by '+ userInfo.getFirstName();
        Test.startTest();
        update acc;
        Test.stopTest();
        
        try{
            delete acc;
        } catch(DMLexception e)
        {
            system.assert(e.getMessage().contains('You Cannot Delete the Account Record'),'You Cannot Delete the Account Record');                       
        }
    }
    
}