Catalog program

[ITgirl2010]

I have been given this program that maintains a catalog of items

'''maintain a catalog'''

def main(): 
    global catalog 

    loadCatalog() 
    while True: 
        pick = showMenu() 
        if pick == 0: 
            break 
        elif pick == 1: 
            sellItem() 
        elif pick == 2: 
            buyItem() 
        else: 
            print "Invalid selection" 
    saveCatalog() 

def showMenu(): 
    global catalog 

    while True: 
        print "Catalog:\n\t%6s %12s %8s %8s" % ( "ItemID", "Item", "Price", "Stock" ) 
        for k in catalog.keys(): 
            print "\t%6d %12s %8s %8d" % (k,catalog[k][0], str("$%0.2f" % catalog[k][1]), catalog[k][2]) 

        try: 
            pick = int(raw_input(''' 
Enter selection: 
0 - Quit 
1 - sell Item 
2 - buy Item 

Selection : ''' )) 
        except: 
            print "Pick must be an integer\n" 
            continue 
        return pick 

def sellItem(): 
    global catalog 
    print "sellItem" 

    try: 
        itemID = int(raw_input("Which item? ")) 
        if itemID in catalog.keys(): 
            howMany = int(raw_input("How many? ")) 
            if 0 < howMany <= catalog[itemID][2]: 
                catalog[itemID][2] -= howMany 
                print "Price for %d %s is $%0.2f" % ( howMany, catalog[itemID][0],catalog[itemID][1]*howMany ) 
            else: 
                print "Can't sell %d %s" % ( howMany, catalog[itemID][0] ) 
        else: 
            print "Invalid itemID" 
    except: 
        print "Bad value entered" 
    print 

def buyItem(): 
    global catalog 
    print "buyItem" 
    try: 
        itemID = int(raw_input("Which item? ")) 
        if itemID in catalog.keys(): 
            howMany = int(raw_input("How many? ")) 
            if 0 < howMany: 
                catalog[itemID][2] += howMany 
            else: 
                print "Can't buy %d %s" % ( howMany, catalog[itemID][0] ) 
        else: 
            print "Invalid itemID" 
    except: 
        print "Bad value entered" 
    print 

def loadCatalog(): 
    global catalog 
    catalog = { 1:["Bread", 1.50, 10 ], 2:["Cheese", 5.00, 5], 3:["Apples", 2.50,12] } 

def saveCatalog(): 
    global catalog 
    pass 

if __name__ == "__main__": 
    main()

Explain this statement:
print "\t%6d %12s %8s %8d" % (k,catalog[k][0], str("$%0.2f" % catalog[k][1]), catalog[k][2])

The program need to be able to modify the price of an item,and it needs to load the first catalog items from a file and then the save the file.

Any help would be great!!!