What kind of bike are you looking for? Your post is in the Road Bike forum, but the bike you're looking at is a BMX.

If you're really looking for a road bike, this chart is a starting point for figuring out what size you should be looking for based on your height and cycling inseam. Your cycling inseam is your leg length, not your pants inseam as explained on the chart. The chart is for frames with traditional geometry (horizontal top tube), and the frame size is based on the length of the seat tube from the center of the crank to the very top of seat tube (where the seatpost is inserted).