These pictures, taken from Wikipedia, should prove resourceful to learning peasant multiplication.
But as an example, I will do one for show.
Equation is written at top. Values in left column are halved; with decimal placements removed and rounded to the lower number. Right column values are doubled. Do this until you get to 1.
Does not apply but worth noting for any future reference for math equations: Any odd should turn even, and any even should remain the same. No need to worry about anything to do with decimal placement when doubling.
35 * 21
Scratch out right column value if left column counterpart is an even number.
Values from right column that are not scratched out are added: 21 + 42 + 672 = 735
Punch equation into your calculator, and you will see 35 * 21, is indeed 735.