Please explain each code. I want to understand it.

Its queue lab. c lang

/* Free all storage used by queue */ 

void q_free(queue_t *q) 

{ 

 /* How about freeing the list elements and the strings? */ 

if(q == NULL) 

return; 

if(q->head != NULL) 

{ 

list_ele_t *present = q->head; // why do we have a present and tempor? 

list_ele_t *tempor = NULL; 

while(present) 

{ 

tempor = present->next; // can you explain these codes below? 

free(present->value); // I understand that using "present" goes through the queue, but explain an each line please

free(present); 

present = tempor; 

 } 

 } 

 free(q); 

 }