1) Arrange the data in order, least to greatest:
65, 68, 68, 70, 70, 72, 72, 74, 76, 76, 76, 78, 80, 84, 86.
2) Find the median which in this case is 74, because there are 7 data elements on either side, so 74 is central. This median is also known as Q2 (Q=quartile).
3) Q1 is the median of the data to the left of 74 and Q3 the median to its right. Q1=70, Q3=78.
Now we can draw the box which goes from Q1 to Q3 (length=78-70=8) with Q2 inside the box. The height of the box doesn't matter. You could make it 2 units high.
4) The whiskers join the lowest value 65 and the highest value 86 to the box. You can draw the box to scale if you like. The range is 65 to 86, so, since 65 is the lowest number this could be the zero position on a line while 86 would be 86-65=21 on the same line. So the length of the line is 21 units, and the box would start at 5 and end at 13. The whiskers each join the box 1 unit high from its base.