From child-Parent soql
----------------------------
Parent = college
child =student(lookup with parent)
relation =Students

written query as

for(Student__c s:[select Name,college__r.Name,CollegeName__c from student__c])
{
  system.debug('student Name:'+s.Name+'     college Name:'+s.college__r.Name);
}

but error as

Line: 3, Column: 18
select Name,college__r.Name,CollegeName__c from ^ ERROR at Row:1:Column:13 Didn't understand relationship 'college__r'