This video is about changing fractions to decimals. The teacher uses 1/2 and 1/3 as his examples.
The first one, changing 1/2 to a decimal. First step is to divide your denominator into your numerator. So, you divide 2 into 1 and add the decimal to your 1 because 2 does not go into one as a whole. Add a zero after your decimal. Put your decimal above, as well. Then, divide 10 by 2, which equals 5. Your answer goes above the last numeral (the 0), which gives you .5 .
In the second example of 2/3, you divide 3 into 2. Add a decimal, and then a 0. 3 goes into 20 six times to equal 18. Subtract 18 from 20 and bring that down and you get 2, add another 0 and divide that by 3. It is 6 again. 3 X 6 is 18, again. It continues in this pattern, so therefore, you put three dots to indicate that it is an infinite number. Your answer is .666.