All points are of the form (x,y) where you list x first and then y second. The order is very important. The x axis is the horizontal number line. Since the first number of (1, 12.5) is 1 this means x = 1 indicating you draw a vertical line through 1 on the x axis as shown in figure 1. This vertical line is shown in red.
The second number is 12.5 so y = 12.5; draw a horizontal line through 12.5 on the y axis. The y axis is the vertical axis. The horizontal line is shown in blue.
The horizontal and vertical lines drawn will meet up at the location (1, 12.5) which is marked in purple. Think of it like an address or perhaps like you're playing the game battleship; however, instead of calling out something like "E5", you just list 2 numbers to help pinpoint an exact location.
Side Note: after you located the point (1, 12.5) you can erase the red vertical line and the blue horizontal line, as they are helper lines to make locating a bit easier. After you get the hang of coordinates, you'll be able to visually locate points without these horizontal and vertical guidelines.