There are lots of different ways.
perhaps the easiest to understand uses the distributive property
12 = 10 + 2
13 = 10 + 3
(10 + 2) (10 + 3)
= 10 (10+3) + 2 (10+3)
= 100 + 30 + 20 + 6
= 100 + 50 + 6
= 156
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You can shorten that by saying
10(13) + 2(13)
= 130 + 26
= 156
How do you multiply 12 times 13 step by step step
2 answers
Another way (watch the video, then try it with your numbers):
http://www.khanacademy.org/math/arithmetic-home/multiply-divide/multi-digit-mult/v/multiplying-whole-numbers-and-applications-2
http://www.khanacademy.org/math/arithmetic-home/multiply-divide/multi-digit-mult/v/multiplying-whole-numbers-and-applications-2