Let's get this math done. We have 12 and we're going to multiply it by 13. This is the same as taking 12 and adding it to itself 13 times.
Step 1: 0 + 12 = 12
Step 2: 12 + 12 = 24
Step 3: 24 + 12 = 36
Step 4: 36 + 12 = 48
Step 5: 48 + 12 = 60
Step 6: 60 + 12 = 72
Step 7: 72 + 12 = 84
Step 8: 84 + 12 = 96
Step 9: 96 + 12 = 108
Step 10: 108 + 12 = 120
Step 11: 120 + 12 = 132
Step 12: 132 + 12 = 144
Step 13: 144 + 12 = 156

So, 12*13 = 156