Start by writing them in ascending order
7, 8, 9, 9, 10, 11, 11, 12, 14, 15, 15, 16, 19
The median (middle number) is the second 11. So look at the first half of the numbers (7, 8, 9, 9, 10, 11) and find the middle number there. Since there are 6 numbers, you average the middle two. Conveniently, they are both 9, so that is Q1. 25% of your numbers are below this mark, and 75% of your numbers are above this mark.
Let me know if you have any questions.